Mapping Gaps in Solid Waste, Wastewater, and Biosolids Education: A National Curriculum Audit of Greek Primary Teacher Education

1. Introduction

Waste management has become a defining environmental and public-health challenge in the transition toward more circular societies. Although definitions vary, circular economy frameworks generally seek to replace linear production and disposal patterns with systems that reduce resource consumption, retain material value, and close resource loops through reuse, recycling, recovery, and related strategies [1,2]. Global municipal solid waste generation is projected to increase from approximately 2.1 billion tonnes in 2023 to 3.8 billion tonnes by 2050, while the economic, health, climate, and ecosystem costs associated with inadequate management are expected to rise substantially [3]. Within contemporary waste policy and circular-economy frameworks, the waste hierarchy prioritises prevention and reduction, followed by reuse, recycling, recovery, and, as the least preferred option, final disposal [4]. This hierarchy is conceptually broader than the familiar act of placing materials in a recycling bin. It requires citizens to understand how consumption, waste prevention, source separation, treatment, resource recovery, and disposal are connected.

A parallel transformation is occurring in the wastewater sector. Recent analyses of the recast European Union framework for urban wastewater treatment highlight the need for more advanced treatment, improved control of pharmaceuticals and other micropollutants, and risk-based approaches to wastewater management [5]. Beyond pollution control, municipal wastewater treatment plants are increasingly conceptualised as resource-recovery facilities capable of recovering water, energy, nutrients, and other valuable products, although important technological, economic, and market barriers remain [6]. Wastewater treatment also generates sewage sludge, which, following appropriate treatment, may be converted into biosolids and managed as a potential source of organic matter, nutrients, and energy. Available management pathways include agricultural use, thermal treatment, disposal, and different forms of material or energy recovery, each involving distinct environmental benefits and risks [7,8]. Beneficial reuse must therefore be balanced against concerns involving pathogens, metals, pharmaceuticals, and other emerging organic contaminants [9,10]. Solid waste, wastewater, and biosolids should therefore not be treated as unrelated technical topics. Together, they illustrate the transition from linear collection-treatment-disposal systems toward integrated resource recovery. They also provide accessible educational contexts through which learners can examine environmental health, technology, consumption, agriculture, risk, and civic decision-making.

Education is expected to support this transition. UNESCO's Education for Sustainable Development for 2030 framework calls for learning that enables people to make informed decisions and participate in individual and collective action for sustainability [11]. A systematic review of 158 peer-reviewed publications identified Teacher Education for Sustainable Development as a growing research field concerned with the design of learning environments, learner attributes, assessment of learning outcomes, systems change, and future directions for teacher education [12]. Earlier research also warned that environmental education can become diluted when it is treated as a peripheral rather than an integral component of teacher preparation [13]. These expectations are particularly important in primary education, where teachers mediate children's first systematic encounters with environmental concepts and everyday environmental practices. The objective is not simply to transmit information about pollution or recycling. The action-competence tradition argues that environmental education should enable learners to investigate problems, assess alternative courses of action, participate in decision-making, and act on issues affecting their lives and communities [14]. This distinction is important because environmental awareness and factual knowledge alone do not reliably produce pro-environmental behaviour. Behaviour is also shaped by motivations, perceived costs and benefits, social norms, habits, psychological barriers, infrastructure, and other contextual conditions [15,16].

Whether future teachers can support such learning depends partly on the opportunities offered during their initial university preparation. Studies of pre-service teachers have identified heterogeneous conceptions of sustainability and uneven levels of environmental literacy at the beginning of teacher education, reinforcing the need for relevant preparation to be explicit rather than assumed [17,18]. A synthesis of the international literature on sustainability in teacher education identified four recurring curricular approaches: broad integration across the programme, a dedicated compulsory course, the inclusion of sustainability within another compulsory course, and a dedicated elective course [19]. These arrangements do not provide equivalent educational opportunities. Preparing teachers to implement education for sustainable development also requires more than exposure to general sustainability concepts. It involves the development of content knowledge, pedagogical content knowledge, motivational dispositions, and opportunities to translate sustainability competencies into everyday school practice [20,21,22]. Compulsory provision or programme-wide integration can establish a common baseline of preparation, whereas elective provision reaches only the students who choose the relevant course. Effective preparation also appears to benefit from connections among the personal, professional, social, and structural dimensions of learning [23]. At the institutional level, whole-institution approaches require coherence among the formal curriculum, organisational practices, professional learning, governance, and community engagement [24]. Consequently, the appearance of a general environmental course title cannot by itself establish whether future teachers encounter specific waste streams, the waste hierarchy, wastewater treatment, biosolids management, or the principles of circular resource recovery.

This issue is particularly relevant in Greece. Environmental education has a substantial history within Greek schools, but its implementation has often depended on local initiatives and the commitment of individual educators rather than on consistent and compulsory curricular integration [25]. More recent research has also identified pedagogical, organisational, structural, and financial barriers affecting the implementation of environmental education programmes in Greek schools [26]. Waste-management education appears to face additional difficulties. A national study involving 332 Greek secondary-school teachers reported moderate-to-low perceived ability to implement waste-management education, greater confidence in addressing solid waste than wastewater, and a tendency to prioritise recycling over waste prevention [27]. A subsequent study of Greek pre-service teachers similarly identified basic familiarity with common waste-management concepts but weaker understanding of specialised terminology, limited confidence regarding wastewater, and comparatively low engagement with practices such as composting and specialised waste collection [28]. These findings suggest a preparedness problem, but survey responses alone cannot establish whether it is associated with the formal learning opportunities provided by teacher-education curricula.

Curriculum mapping offers a complementary institutional perspective by making visible what content is formally included, where it appears within a programme, and whether all students are guaranteed exposure to it [29]. Official study guides and course descriptions do not reveal everything instructors may teach or everything students ultimately learn. Instead, they represent the intended and publicly documented curriculum. Nevertheless, they specify formal course availability, status, learning outcomes, and content and are therefore appropriate sources for assessing whether preparation is systematic, optional, fragmented, or absent. The distinction between the documented curriculum and actual teacher knowledge is critical. The absence of a topic from official documentation does not prove that graduates possess no relevant knowledge, just as the appearance of a topic does not prove that students have mastered it. Curriculum documents can, however, establish whether a programme formally guarantees students an opportunity to develop such knowledge.

To the authors' knowledge, no previous national audit has compared the documented treatment of solid waste, wastewater, and biosolids across all Greek undergraduate programmes preparing primary-school teachers. Previous Greek studies have primarily examined teachers' or pre-service teachers' knowledge, attitudes, confidence, and reported practices [27,28]. The institutional dimension remains insufficiently examined: whether the formal curricula responsible for preparing future primary teachers systematically address the interconnected management of solid waste, wastewater, and biosolids.

The present study addresses this gap through a census-based curriculum audit of the official study guides and course descriptions of all nine Greek public undergraduate departments that prepare teachers for primary education. It examines: (i) whether each programme provides documented learning opportunities related to solid waste, wastewater, or biosolids; (ii) whether relevant exposure is compulsory, compulsory-choice, or elective; and (iii) whether these topics receive substantive treatment or appear only incidentally within broader environmental courses. Solid waste is used as a comparative benchmark for assessing the relative curricular visibility of wastewater and biosolids. By identifying whether future primary teachers receive documented preparation to explain wastewater treatment, treatment residuals, resource recovery, and associated risk-benefit trade-offs, the study contributes an educational and public-understanding perspective to the field of wastewater and biosolids management.

2. Materials and Methods

2.1. Study Design and Scope

This study employed a cross-sectional, census-based document analysis of the publicly documented undergraduate curricula of Greek primary teacher education programmes. Document analysis was selected because official study guides, programme catalogues, and course descriptions constitute formal records of the intended curriculum and allow systematic comparison across institutions [30]. The analysis did not examine the enacted curriculum, informal teaching practices, student participation in elective courses, or graduates' acquired knowledge.

The study population comprised all nine public undergraduate university programmes in Greece that lead to qualification as a primary-school teacher. The completeness of the national census was verified by cross-checking official departmental listings and undergraduate programme documentation and confirming the eligibility of each included degree. The nine eligible programmes and their corresponding official source records are presented in Table 1 and in the deposited source register [31]. Because the complete national population was examined, no institutional sampling was undertaken. Postgraduate programmes, early-childhood education departments, secondary-subject teacher programmes, continuing professional development courses, and non-degree training activities were excluded.The programme was the principal unit of analysis for estimating national curriculum coverage. Individual courses constituted the evidence-bearing subunits used to determine whether each programme included explicit content related to solid waste, wastewater, or biosolids.

2.2. Programme Census and Document Corpus

Official documentation was retrieved and verified through university and departmental websites up to 29 August 2026. For each institution, the most recent complete undergraduate study guide, course-description volume, programme catalogue, or official course page available by the audit cut-off date was examined. The reviewed documentation covered the academic years 2025-2026 and 2026-2027 because the departments did not publish or update their documentation according to a uniform schedule.

The corpus included Greek-language and English-language documents. When information was distributed across more than one official source, such as a programme catalogue and a separate course-description volume, the sources were examined together. Documentation was considered eligible when it described the undergraduate programme structure, course status, learning outcomes, syllabus content, teaching activities, or assessment. Institutional mission statements, promotional material, postgraduate modules, and documents unrelated to the qualifying undergraduate programme were excluded.

All coding decisions were made from the original-language text. Any English translations of Greek course titles or evidence summaries used for reporting were verified by the primary researcher against the original wording.

The final source corpus is presented in Table 1. Full bibliographic and access information, official URLs, source identifiers, and file names are provided in the deposited source register [31].

2.3. Search Strategy

Each eligible document was searched electronically using predefined Greek and English terms and word stems. The search strategy covered five related conceptual groups:

• solid waste and refuse;
• recycling, reuse, composting, and circular economy;
• wastewater, sewage, and liquid waste;
• wastewater treatment and resource recovery; and
• sewage sludge and biosolids.

The principal Greek search roots were:

αποβλητ, απορρίμμ, σκουπιδ, ανακύκλ, επαναχρησιμοπ, κομποστ, κυκλικ, λύμα, υγρά απόβλητα, ιλύ, and βιοστερε.

The corresponding English terms included:

waste, wastes, refuse, rubbish, solid waste, municipal waste, recycling, reuse, composting, circular economy, wastewater, sewage, liquid waste, wastewater treatment, sludge, sewage sludge, and biosolids.

The primary audit used the principal Greek roots and English terms listed above. Keyword screening was supplemented by manual review of programme course lists and plausible course titles to identify potentially relevant courses not retrieved through the principal terms. The independent audit used an expanded set of 51 Greek and English terms or roots, each applied separately to 19 searchable official sources. The complete expanded term set and all 969 logged source-term searches are preserved in the unchanged independent audit workbook deposited with the replication package [31].

Both audits applied the same eligibility and domain-coding rules. Search terms were used only to locate potentially relevant passages, and no course or programme was coded automatically from a keyword hit. Potentially relevant occurrences were examined in context by reviewing course titles, learning outcomes, syllabi, teaching units, learning activities, and, where available, assessment requirements. This contextual review distinguished target-domain content from unrelated uses of the same vocabulary, such as biological nutrient recycling or generic references to environmental pollution.

2.4. Eligibility and Coding Rules

A course was retained only when its official description contained explicit educational content concerning at least one of the three target domains. Generic references to sustainability, environmental awareness, pollution, natural-resource conservation, urban environmental problems, project-based learning, or undifferentiated waste were insufficient unless solid waste, wastewater, biosolids, or a qualifying domain-specific management operation was explicitly identified.

The operational definitions are presented in Table 2.

For this audit, a compulsory-choice course was defined as a course selected from a required basket of alternative courses. Such a course was not treated as guaranteeing exposure when students could satisfy the requirement by selecting other, non-relevant courses.

One borderline case was retained as substantive solid-waste exposure because the official learning outcomes referred directly to recycling and the syllabus included "Art and Recycling" as a separate course theme. This combination satisfied the predefined depth criterion of an explicit learning outcome together with a distinct relevant teaching theme. The course was nevertheless not treated as equivalent to a dedicated waste-management course, and the decision was recorded transparently in the course-level evidence file.

For programmes coded as negative, the interpretation was limited to the statement that no explicit qualifying content was identified in the reviewed public documents. A negative code was not interpreted as evidence that lecturers never discuss the topic informally.

2.5. Course-Level Data Extraction

For every retained course, the following information was extracted:

• institution and programme identifier;
• course code and title;
• compulsory, compulsory-choice, elective, or unreported status;
• semester and ECTS credits, where reported;
• presence of solid-waste, wastewater, and biosolids content;
• source identifier and location within the document;
• a short evidential excerpt or faithful summary; and
• depth of treatment.

Depth was classified as either "substantive" or "incidental". Content was coded as substantive when the course included a dedicated teaching unit, an explicit learning outcome, several connected syllabus items, or sustained treatment of the domain. An isolated example or brief reference embedded within a broader course was classified as incidental. Depth did not alter the binary programme-level result but was retained to distinguish meaningful treatment from limited exposure.

No composite curriculum score was calculated because the presence of solid waste, wastewater, and biosolids content represents conceptually distinct educational opportunities that should not be collapsed into a single numerical index.

2.6. Independent Reliability Assessment

After completion of the primary coding, a second researcher conducted a full independent audit of all nine programmes. To preserve independence, the second researcher did not consult the manuscript, the primary programme classifications, the deposited dataset, the published coding protocol, or the previously reported results before completing the audit.

The independent audit covered 19 unique searchable official sources. Each of 51 predefined Greek and English search terms or roots was applied separately to every source, producing 969 documented source-term searches. Potentially relevant occurrences were examined in context, and programme course lists were subsequently reviewed manually to identify plausible courses that might not have been retrieved through keyword searching.

The second researcher independently coded five binary programme-level variables: any relevant content, solid waste, wastewater, biosolids, and guaranteed compulsory exposure. This produced 45 paired pre-consensus decisions. Agreement was observed in 40 of the 45 decisions (88.9%). Pooled Cohen's kappa, calculated to adjust observed agreement for agreement expected by chance, was 0.72 [32,33]. The pooled kappa is reported as a descriptive summary across all paired binary decisions. Because the variables were conceptually related and differed in prevalence, the variable-specific agreement and kappa values should be considered alongside the pooled estimate. Agreement was 7/9 for any relevant content, 7/9 for solid waste, 8/9 for wastewater, and 9/9 for both biosolids and guaranteed compulsory exposure. Cohen's kappa was not estimable for biosolids because both coders classified all nine programmes as negative for that domain.

The five binary discrepancies arose from two programme-level cases. At the University of the Aegean, the independent audit excluded a generic reference to waste because it did not identify a target domain or qualifying management operation. At the University of Thessaly, the independent audit identified a previously missed course containing explicit references to sewage, refuse, and waste. The discrepancies were resolved through consensus adjudication against the predefined rules and the original official sources. Course-status metadata for the five retained courses were subsequently verified separately against the official programme tables.

2.7. Data Analysis and Reproducibility

Analysis was descriptive because the study covered the entire population of nine eligible programmes rather than a sample intended for statistical generalisation. For each binary indicator, the number of programmes coded "Yes" was divided by nine and reported as a count and percentage. No inferential statistical tests were performed.

The analysis also compared course status and depth to determine whether documented exposure was compulsory, compulsory-choice, elective, substantive, or incidental. The final consensus dataset, source register, course-level evidence, pre-consensus reliability comparison, unchanged independent audit workbook, coding protocol, and reproducible base-R analysis script are deposited in Zenodo as version 1.2 [31].

The deposited source register provides links to the official university documentation. The full university study guides are not redistributed because they remain the intellectual property of their issuing institutions. Only short excerpts or evidence summaries required to audit the coding decisions are included in the dataset.

2.8. Ethical Considerations

The study analysed publicly available institutional curriculum documents and did not involve human participants, personal data, surveys, interviews, or classroom observations. Institutional review board approval and informed consent were therefore not applicable. The findings concern the intended and publicly documented curriculum and should not be interpreted as an assessment of individual lecturers, students, graduates, or practising teachers.

2.9. Use of Generative Artificial Intelligence Tools

OpenAI ChatGPT and Codex were used during the research and manuscript-preparation process to assist with text extraction from the collected documents, organisation of source material, preparation and checking of reproducibility files and analysis code, manuscript structuring, and English-language editing. The tools did not make final eligibility, inclusion, exclusion, or coding decisions. All keyword matches and contextual evidence used in the primary audit were reviewed by the primary researcher, and the final primary coding decisions were made by the authors according to the predefined protocol. A second researcher subsequently conducted a full independent audit of all nine programmes without consulting the primary classifications or previously reported results. All discrepancies were resolved by the authors through consensus adjudication against the predefined rules and original official sources. All numerical results, references, interpretations, and AI-assisted text were subsequently reviewed and approved by the authors, who retain full responsibility for the accuracy and integrity of the study.

3. Results

3.1. National Programme-Level Pattern

The complete national audit identified five programmes containing at least one course with explicit content related to solid waste, wastewater, or biosolids. This corresponded to 55.6% of the nine eligible programmes. Four programmes (44.4%) documented explicit solid-waste content, while three (33.3%) documented wastewater content. No explicit reference to biosolids, sewage sludge, or wastewater sludge was identified in any programme.

One of the nine programmes (11.1%) guaranteed compulsory exposure to relevant content through a required course addressing both solid and liquid waste. Among the five retained courses, one was compulsory, one was compulsory-choice, and three were elective. Consequently, guaranteed exposure was identified in only one programme, while students in the remaining eight programmes could complete their studies without being required to encounter explicit content on solid waste, wastewater, or biosolids.

The distribution of the target domains was uneven. Two programmes contained solid-waste content without wastewater content, one contained wastewater content without solid-waste content, and two contained both solid-waste and wastewater content. Therefore, two programmes documented formal coverage of both solid and liquid waste within the same relevant course. The programme-level results are presented in Table 3 and correspond to the consensus dataset deposited in Zenodo [31].

3.2. Course-Level Evidence and Depth

Exactly one relevant course was identified in each of the five positive programmes, producing a total of five retained courses. Four courses were classified as providing substantive coverage, while one was classified as incidental. Nevertheless, even substantive coverage remained embedded within broader courses rather than constituting a dedicated course focused primarily on waste management, wastewater, or biosolids.

At Aristotle University of Thessaloniki, the elective course EPM129, "Visual Arts and Sustainable Development in Education", referred explicitly to recycling in its learning outcomes and included "Art and Recycling" as a separate course theme. The combination of an explicit learning outcome and a distinct relevant teaching theme supported its classification as substantive solid-waste exposure, although the course was not primarily focused on waste-management systems.

The University of Crete provided the most detailed solid-waste content identified in the audit. The elective course E02 10, "Ecology", explicitly addressed municipal solid waste and management through dumps, incineration, sanitary landfill, reuse, and recycling. The presence of several connected management options supported its classification as substantive coverage.

At the University of Thessaly, the elective course ΦΕ1301, "Earth Science Concepts in Education", included the explicit thematic item "Human and environment: Natural resources. Sewage, refuse and waste." The references to sewage and refuse satisfied the wastewater and solid-waste inclusion rules, respectively. Because the target content appeared as one brief item within a broader Earth-science education course, it was classified as incidental rather than substantive.

At the University of Ioannina, the compulsory course ΔΕΥ065, "Concepts and Issues of Environment and Sustainability", was offered in the second semester for 4 ECTS. Its syllabus identified the management of water and of solid and liquid waste as central course issues. It was one of two retained courses covering both solid-waste and wastewater domains and the only course that guaranteed relevant exposure for every student in its programme. No explicit biosolids or sewage-sludge content was identified.

At Democritus University of Thrace, the compulsory-choice course 7ΕΓ4, "Environmental Chemistry in Education", included methods for controlling or treating liquid and gaseous wastes and a complete teaching unit on liquid-waste treatment. This constituted the clearest wastewater-treatment content identified in the national corpus. Because the course was offered within a compulsory-choice structure, it did not guarantee exposure for every student. No explicit solid-waste, biosolids, or sewage-sludge content was identified in the course description.

The characteristics of the five retained courses are summarised in Table 4.

3.3. Negative Programmes and Boundaries of the Findings

No explicit qualifying content was identified in the reviewed programme documentation of the National and Kapodistrian University of Athens, the University of the Aegean, the University of Patras, or the University of Western Macedonia.

These negative classifications did not necessarily indicate an absence of environmental education or related environmental topics. At the University of the Aegean, for example, one course included the generic item "waste and its management". However, the item did not specify solid waste, wastewater, biosolids, or a qualifying domain-specific management operation. Under the predefined conservative rules, it was therefore excluded rather than assigned to a target domain through inference.

No programme was classified as negative solely because programme documentation was unavailable. Eligible official documentation was reviewed for all nine programmes. The negative results therefore indicate that no explicit target-domain content was identified in the examined public documentation, not that the topics are never discussed by lecturers or encountered by students.

3.4. Compulsory Exposure and Curricular Position

The five retained courses comprised one compulsory course, one compulsory-choice course, and three electives. The compulsory course at the University of Ioannina guaranteed relevant exposure within that programme. The compulsory-choice course at Democritus University of Thrace did not guarantee exposure because students could satisfy the relevant choice requirement through other courses. No other compulsory course containing explicit solid-waste, wastewater, or biosolids content was identified.

Accordingly, guaranteed compulsory exposure was identified in 1 of the 9 programmes (11.1%). The audit therefore distinguished between curriculum availability and curriculum entitlement: relevant learning opportunities existed in five programmes, but only one programme formally guaranteed that every graduate would encounter qualifying content.

The retained content was consistently embedded within broader disciplinary or pedagogical contexts. These included visual arts and sustainable development, ecology, environment and sustainability, environmental chemistry, and Earth-science education. None of the identified courses had solid waste, wastewater management, sludge, or biosolids as its primary course title.

3.5. Independent Coding Reliability

The independent audit covered all nine programmes and five binary programme-level variables, producing 45 paired pre-consensus decisions. The variables were any relevant content, solid waste, wastewater, biosolids, and guaranteed compulsory exposure.

The two coders agreed on 40 of the 45 decisions, corresponding to 88.9% observed agreement. Pooled Cohen's kappa was 0.72. Agreement was 7/9 for any relevant content, 7/9 for solid waste, 8/9 for wastewater, and 9/9 for both biosolids and guaranteed compulsory exposure.

Table 5. Results of the independent reliability assessment.

Variable	Agreements	Decisions	Observed agreement	Cohen's kappa
Any relevant content	7	9	77.8 %	0.55
Solid waste	7	9	77.8 %	0.55
Wastewater	8	9	88.9 %	0.73
Biosolids	9	9	100 %	Not estimable
Guaranteed compulsory exposure	9	9	100 %	1.00
Pooled decisions	40	45	88.9%	0.72

Table 5. Results of the independent reliability assessment.

Variable	Agreements	Decisions	Observed agreement	Cohen's kappa
Any relevant content	7	9	77.8 %	0.55
Solid waste	7	9	77.8 %	0.55
Wastewater	8	9	88.9 %	0.73
Biosolids	9	9	100 %	Not estimable
Guaranteed compulsory exposure	9	9	100 %	1.00
Pooled decisions	40	45	88.9%	0.72

Pooled observed agreement was 88.9%, and pooled Cohen's kappa was 0.72. The five binary discrepancies arose from two programme-level cases: the classification of a generic waste item at the University of the Aegean and the identification of a previously missed course at the University of Thessaly. Consensus adjudication excluded the Aegean item and retained the Thessaly course for solid waste and wastewater. The final consensus results are reported in Table 3 and Table 4.

4. Discussion

4.1. Presence without Entitlement

The central finding is not that waste-related education is entirely absent from Greek primary teacher preparation. Explicit content was identified in five of the nine programmes, including substantive content in four of the five retained courses. A claim of complete curricular absence would therefore be inaccurate. The more consequential finding is that compulsory exposure was rare: among the five relevant courses, one was compulsory, one was compulsory-choice, and three were elective. Only the University of Ioannina programme guaranteed that every graduate would encounter explicit content on solid or liquid waste, while none of the nine programmes guaranteed exposure to biosolids or sewage sludge.

This distinction between availability and entitlement is important. A compulsory course can establish a common learning opportunity for all students within a programme, whereas compulsory-choice and elective courses do not necessarily ensure that every student encounters the relevant content. Sustainability can be embedded in teacher education through programme-wide integration, compulsory courses, components of compulsory courses, compulsory-choice structures, or electives, but these arrangements do not provide equivalent coverage [19]. In the present audit, the compulsory course at the University of Ioannina established a documented entitlement within one programme, while provision in the other four positive programmes depended on students' course selections.

The results consequently suggest a fragmented national pattern. Five programmes contained a relevant learning opportunity, but each included only one qualifying course, and every instance was embedded within a broader disciplinary or pedagogical context. Curriculum mapping is useful in this situation because isolated course-level content may appear adequate when examined individually while remaining discontinuous or non-compulsory at programme level [29]. The documented curriculum established a common baseline of relevant waste-management learning in only one of the nine programmes.

This pattern should not be interpreted as evidence that graduates possess no relevant knowledge. Students may acquire knowledge through other courses, personal experience, school placements, informal discussion, or participation in environmental activities. Similarly, lecturers may teach examples that do not appear in official descriptions. The defensible conclusion is narrower: the publicly documented curriculum established guaranteed exposure to relevant waste content in only one of the nine programmes and did not establish guaranteed exposure to biosolids or sewage sludge in any programme.

4.2. Beyond Recycling, but Not Yet across the Waste Hierarchy

The findings provide a more nuanced account of waste education in Greek primary teacher preparation. The documented provision was not limited exclusively to placing recyclable materials in separate bins. The University of Crete course addressed several municipal solid-waste management options, including dumps, incineration, sanitary landfill, reuse, and recycling, while the University of Ioannina connected the management of solid and liquid waste. These examples extended beyond a purely symbolic treatment of recycling, although their curricular availability and depth remained uneven.

Nevertheless, the documented provision remained selective and incomplete. Recycling was a prominent theme, including an explicit learning outcome and a separate "Art and Recycling" course theme at Aristotle University of Thessaloniki. None of the documented evidence for the five retained courses identified waste prevention as a distinct learning topic. Because waste prevention was not coded as a separate programme-level variable, this pattern should be interpreted as a course-level observation rather than as evidence of its national absence. The retained course evidence was therefore more strongly oriented toward managing waste after its generation than toward the earlier stages of avoiding and reducing waste.

This imbalance matters educationally. Formal education can strengthen awareness and understanding of solid-waste management, but its contribution depends on the breadth and quality of the learning opportunities provided. Recycling can offer an accessible entry point for young learners; however, restricting instruction primarily to recycling risks obscuring waste prevention, reuse, treatment, recovery, disposal, and the wider systems through which waste is generated and managed [34]. When recycling becomes the dominant or only visible frame, students may acquire a simplified understanding in which correct disposal substitutes for examining why waste is generated and how production and consumption choices might be changed.

The action-competence tradition in environmental education emphasises learners' capacity to investigate problems, consider alternatives, participate in decisions, and take informed action [14]. Such an approach requires more than teaching a predetermined environmentally desirable behaviour. It requires opportunities to examine competing options, practical constraints, environmental consequences, and the roles of citizens, institutions, businesses, and public authorities. The well-established gap between environmental awareness and behaviour also demonstrates why providing information or promoting a single action cannot by itself guarantee broader environmental change [35].

The present audit did not examine how the identified topics were taught and therefore cannot determine whether the courses adopted an action-oriented or behaviour-focused approach. It does, however, show that the documented content available to future primary teachers rarely presented the complete waste hierarchy as a coherent educational framework.

4.3. The Wastewater and Biosolids Gap

Wastewater received less curricular attention than solid waste. Explicit wastewater content was identified in three programmes, compared with solid-waste content in four. Only the Democritus University of Thrace course contained a clearly identifiable teaching unit on liquid-waste treatment. The University of Ioannina and the University of Thessaly both connected solid-waste and wastewater content within the same relevant course, although the Thessaly evidence was limited to one incidental thematic item.

This pattern is consistent with earlier Greek research showing greater familiarity and confidence concerning solid waste than wastewater. Greek secondary-school teachers reported higher perceived preparedness for solid-waste education and a stronger emphasis on recycling than on liquid-waste issues [27]. Research involving Greek pre-service teachers similarly identified weaker knowledge and self-efficacy in technically specific waste topics, particularly those associated with wastewater [28].

The convergence between these studies and the curriculum audit is noteworthy but must be interpreted cautiously. The previous studies measured reported knowledge, perceptions, or self-efficacy in different populations, whereas the present study examined institutional documents. The evidence does not establish that limited curricular coverage caused the reported knowledge or confidence patterns. It does, however, identify a plausible structural condition that may contribute to uneven preparation and warrants direct investigation through linked curriculum and competence studies.

The absence of explicit biosolids content from the reviewed documents was the clearest thematic gap. None of the nine programmes explicitly referred to biosolids, sewage sludge, wastewater sludge, sludge treatment, or sludge reuse. This finding is educationally important because wastewater education remains incomplete when treatment residuals are omitted from the documented learning content.

Biosolids provide an educationally valuable example of the complexity of circular-economy decisions. Sewage sludge can contain organic matter and nutrients with potential agricultural value, but its management must also consider pathogens, metals, pharmaceuticals, and other emerging contaminants [10]. The topic therefore connects wastewater treatment with soil, agriculture, food production, public health, risk assessment, regulation, and resource recovery.

Primary teachers do not need the technical preparation of wastewater engineers. However, they require sufficient conceptual understanding to explain that wastewater does not disappear after leaving a household, that treatment produces both treated water and residual materials, and that recovery and reuse involve environmental benefits as well as potential risks. Without this basic systems perspective, school-level wastewater education may stop at water conservation or pollution awareness without examining what treatment actually involves.

4.4. From Fragmented Opportunities to a Minimum Learning Entitlement

The results do not necessarily support the creation of a separate engineering-oriented waste-management course in every primary teacher programme. Such a recommendation could be disproportionate to the professional role of primary teachers and difficult to accommodate within already crowded curricula. A more realistic response would be the establishment of a concise but explicit compulsory learning entitlement within science education, environmental education, or education for sustainable development.

At minimum, every graduate should be able to:

• distinguish waste prevention, reuse, recycling, recovery, and disposal;
• differentiate solid waste, wastewater, and wastewater-treatment residuals;
• describe the basic pathway from waste generation and collection to treatment, recovery, reuse, or final disposal;
• explain in age-appropriate language where wastewater goes and what wastewater treatment produces;
• recognise the potential benefits and risks associated with sludge and biosolids management;
• evaluate school environmental actions without reducing waste education to bin sorting; and
• design inquiry-based, locally relevant, and action-oriented learning activities for primary pupils.

These outcomes could be addressed through a compulsory module rather than a complete stand-alone course. Effective integration requires more than the isolated addition of sustainability content: it should deliberately develop content knowledge, pedagogical content knowledge, motivation, and the capacity to translate sustainability competencies into everyday school practice [20,21,22]. It should also connect personal understanding, professional practice, social participation, and institutional structures [19,23]. Whole-institution approaches similarly emphasise coherence between the formal curriculum, educator development, institutional practices, governance, and community partnerships [24].

A compulsory module could therefore combine conceptual content with assessed pedagogical application. Possible activities include conducting a school waste-prevention audit, comparing prevention and recycling strategies, mapping the local wastewater pathway, examining simplified wastewater-treatment stages, visiting a waste or wastewater facility, evaluating claims about compost and biosolids, or designing an age-appropriate teaching sequence that connects consumption with waste generation and resource recovery.

The key requirement is that practical application should be explicit and assessed rather than assumed from the general presence of project-based learning. A programme may contain strong environmental pedagogy while still failing to provide the subject knowledge required to teach a specific issue accurately. Conversely, technical content without primary-school application may not prepare future teachers to translate that content into meaningful classroom learning. The curriculum therefore needs both domain knowledge and pedagogical transformation.

4.5. Implications for Environmental Education in Greece

The predominantly non-compulsory character of the identified provision should be considered within the broader development of environmental education in Greece. Previous research has shown that implementation has frequently depended on local initiatives, institutional conditions, and the commitment of individual educators [25,26]. The present findings indicate that a similar dependency may begin during initial teacher preparation. Although one programme guaranteed relevant exposure through a compulsory course, provision in the other positive programmes depended on compulsory-choice or elective pathways. A common national baseline was therefore not established across the nine programmes.

This creates the possibility of substantial variation among future teachers. Some may complete an ecology course with substantive solid-waste content, others may encounter wastewater treatment through environmental chemistry, and others may graduate without any explicitly documented exposure to the target domains. Such variation does not mean that graduates are necessarily unprepared, but it makes their documented formal preparation dependent on institutional location and individual course choice.

The findings therefore support curricular coordination rather than standardisation of every course. Universities should retain flexibility in how the entitlement is delivered, but the essential concepts and expected competencies should be identifiable across programmes. This could be supported through shared learning outcomes, open teaching materials, collaboration with municipalities and utilities, and field-based activities involving local waste and wastewater systems.

4.6. Strengths and Limitations

The principal strength of the study is its national coverage. Rather than examining a convenience sample of departments, the audit included the complete population of nine Greek public undergraduate programmes preparing primary-school teachers. The study also applied explicit inclusion rules, distinguished general environmental content from target-specific content, retained course-level evidence, and documented negative decisions.

Transparency and reproducibility were strengthened through the publication of the programme-level data, course-level evidence, source register, coding protocol, pre-consensus reliability comparison, unchanged independent audit workbook, and analysis script [31]. The full independent audit produced agreement on 40 of 45 programme-level binary decisions (88.9%) and a pooled Cohen's kappa of 0.72. It also identified two programme-level cases requiring consensus adjudication, demonstrating the value of independent verification for detecting both over-inclusion and previously missed evidence.

Several limitations must also be acknowledged. First, official documents represent the intended and publicly documented curriculum, not necessarily the curriculum enacted by lecturers or experienced by students. Relevant examples may be taught without appearing in official descriptions, while listed content may receive limited instructional time.

Second, the academic years of the documents were not uniform. The audit used the most recent complete official material available at the defined cut-off date, but the reviewed programme documentation covered the academic years 2025-2026 and 2026-2027. The study therefore provides a time-bounded national snapshot rather than a permanently valid classification.

Third, formal course status does not establish whether a course was offered in every academic year, how the documented content was enacted, or how many students completed it. For compulsory-choice and elective courses, the reviewed documents also did not provide enrolment or completion data. Consequently, the audit can identify documented curriculum availability and programme-level entitlement, but it cannot estimate the actual proportion of graduates who encountered or mastered the relevant content.

Fourth, course descriptions varied in detail. Some provided extensive learning outcomes and weekly teaching units, whereas others offered only brief summaries. Differences in documentary detail may therefore have affected the probability of identifying explicit target-domain content. The use of predefined inclusion criteria, retained course-level evidence, contextual and manual review, and conservative coding reduced this risk but could not eliminate it.

Fifth, the substantive/incidental distinction and the interpretation of borderline terminology involved judgement, even though they were based on predefined rules. The primary and independent audits applied the same eligibility and domain-coding rules but did not use identical search implementations: the independent audit employed an expanded and fully logged set of 51 terms or roots. The agreement statistics should therefore be interpreted as indicators of the reproducibility of the overall audit outcomes, encompassing both evidence retrieval and classification, rather than as measures of coding agreement under identical retrieval procedures. The full independent audit reduced the risk associated with single-coder assessment but did not eliminate interpretive uncertainty. The pooled kappa of 0.72 indicates agreement beyond chance, while the need to adjudicate discrepancies in two programmes confirms that the audit still required contextual judgement.

Sixth, binary programme-level indicators simplify differences in the amount, quality, sequencing, and pedagogical treatment of the content. A programme with a single brief reference and a programme with a full teaching unit both contribute one positive programme-level case, although the course-level depth classification partly addresses this limitation.

Finally, the study cannot determine whether curriculum structure predicts graduate knowledge, teacher self-efficacy, or classroom practice. Establishing such relationships would require course observations, lecturer interviews, student assessments, analysis of teaching materials, and longitudinal research following graduates into schools. A complementary audit of official primary- and secondary-school curricula and textbooks would also be valuable for examining whether the same emphasis on recycling and limited visibility of wastewater and biosolids continues into school education.

5. Conclusions

This national curriculum audit examined the publicly documented undergraduate preparation of primary-school teachers in Greece in relation to solid waste, wastewater, and biosolids. Explicit target-domain content was identified in five of the nine programmes. Solid waste appeared in four programmes, wastewater in three, and biosolids in none. Among the five relevant courses, one was compulsory, one was compulsory-choice, and three were elective. Only one programme guaranteed that every graduate would encounter qualifying waste-related content.

The findings therefore do not support the claim that waste-related education is entirely absent from Greek primary teacher preparation. They support a more precise and educationally significant conclusion: relevant preparation was documented in five programmes but guaranteed in only one, making provision predominantly non-compulsory, institutionally uneven, and thematically fragmented. Solid-waste content was more visible than wastewater content, while no explicit content on wastewater-treatment residuals, sewage sludge, or biosolids was identified in the reviewed curriculum documents.

The curricular pattern also extended beyond a simple recycling-only model in some programmes. The strongest solid-waste course addressed multiple management options, and the clearest wastewater course contained a dedicated liquid-waste treatment unit. Nevertheless, within the five retained courses, waste prevention was not identified as a distinct learning topic; two programmes connected solid and liquid waste within the same relevant course, although one did so only incidentally, and none presented biosolids as part of circular resource recovery.

A proportionate curricular response would not require every future primary teacher to complete an engineering-oriented waste-management course. The findings instead support consideration of a concise compulsory learning entitlement integrating the waste hierarchy, basic wastewater treatment, treatment residuals, resource recovery, and primary-school pedagogy. Such preparation could enable future teachers to move beyond isolated awareness activities and design age-appropriate learning that connects consumption, waste prevention, treatment systems, environmental health, and civic decision-making.

The study concerns the intended and publicly documented curriculum. It does not establish what individual lecturers teach, what students encounter or master through compulsory, compulsory-choice, or elective courses, or how graduates subsequently teach waste-related issues in schools. Future research should combine curriculum analysis with lecturer interviews, course observations, student competence assessments, and analysis of school curricula and textbooks. Such work could determine whether uneven and predominantly non-compulsory initial preparation is associated with later differences in teacher confidence, conceptual understanding, and classroom practice.