Reuse of treated water and sludge from wastewater treatment plants in the Béni Mellal-Khénifra region, Morocco: a critical literature review

Abstract

Background: Morocco is increasingly relying on treated wastewater reuse and sewage sludge valorisation to address structural water stress, climate change, and growing demographic and industrial pressures. In the Béni Mellal-Khénifra region, recent large-scale tertiary wastewater treatment investments by OCP Green Water coexist with a substantial body of research documenting metal contamination of irrigated soils and groundwater. However, these two hydrological realities have not yet been critically integrated. Objectives: This study maps the regional and national research landscape, verifies three hypothesized research gaps, evaluates the credibility of available evidence, and proposes a priority research program for sustainable wastewater reuse and sludge valorisation. Methods: A PRISMA-guided critical literature review was conducted. An exploratory scoping search generated three hypotheses, followed by a formal eight-query identification and selection process that retrieved 63 records and retained 15 primary regional studies. A five-level evidence-validation framework was applied, with mandatory triangulation of quantitative claims derived from institutional or non-peer-reviewed sources. The review also explicitly assessed methodological limitations, source concentration, and the reproducibility of the evidence base. Key limitations included the reliance on open academic sources without systematic access to a single proprietary bibliographic database such as Scopus or Web of Science, the concentration of the regional academic corpus within two overlapping research teams at Sultan Moulay Slimane University, and the reliance of several recent infrastructure estimates on a single institutional source chain without independent audit. The underlying evidence was further limited by small sampling sizes, scarce control groups and longitudinal datasets, and heterogeneous reference thresholds across studies. Results: Three research gaps were largely confirmed. Integrated health–environmental assessment remains incomplete: metal contamination is relatively well documented locally, but emerging contaminants and the integration of antimicrobial resistance with chemical contamination are virtually unexplored. Governance and social acceptability are only partially addressed, with one study assessing farmers’ and residents’ perceptions but none examining institutional governance. Longitudinal contaminant monitoring is absent, and climate coupling remains limited. Most importantly, no published study links the documented historical contamination of irrigated soils with the effects of the new OCP Green Water tertiary treatment infrastructure. A regulatory gap concerning quality standards for sludge intended for agricultural spreading was also identified. The evidence base is further constrained by small samples, limited controls and time series, heterogeneous reference thresholds, and reliance on unaudited institutional infrastructure data. Conclusion: This first integrated regional synthesis provides an evidence-validation framework and a seven-pronged research agenda. It highlights priorities for independent monitoring, integrated contaminant and antimicrobial-resistance assessment, governance research, and sludge regulation before further expansion of wastewater reuse.