This study aimed to assess the agronomic value of solar-dried sludge (SDS) and the transfer of Cr, Ni, Pb, and Cu to wheat (Triticum aestivum) and faba bean (Vicia faba). A greenhouse experiment was performed involving two rates of SDS (15 t/ha and 30 t/ha) from an activated sludge-based wastewater treatment plant. In addition to the single use of an SDS amendment, co-application of SDS and mineral fertilizers was also included to determine the best scenario resulting in high yields and less negative implications on the environment. Data for both wheat and faba bean showed that applying SDS at 30 t/ha led to competitive yields compared to the ones obtained previously, while 15 t/ha of SDS and mineral fertilizers were co-applied. The use of SDS increased soil organic matter, slightly decreased the pH value, and increased soil salinity. The contents of Ni, Cu, and Pb were not significantly affected by the application of SDS. Only Cr showed high soil concentrations in proportion to the increasing rates of SDS. The bioaccumulation of heavy metals in roots was more important in 30 t/ha than that in 15 t/ha amended soil. In the case of wheat, the bioconcentration factor (BCF) root values correspond to the following order: Cr (0.89) >Cu (0.85)> Ni (0.28)> Pb (0.22). In the case of faba bean, BCF roots were observed as follows: Cu (1.04 > Ni (0.37)> Cr (0.16)> Pb (0.15). Wheat excluded Cr, Ni, and Pb from the uptake by shoots, and Cu was translocated from roots to shoots with a percentage of 11% at 30 t/ha of applied SDS. Faba beans demonstrated more important values of HM’s translocation by respecting this order (Ni (37.7%) > cu (30.24%)> Cr (17.59%), while Pb was excluded from the translocation. No significant difference was observed regarding the translocation index when the sludge rate has been duplicated from 15 t/ha to 30 t/ha. Based on these outcomes, SDS used at the rate of 30 t/ha is the best scenario to amend the soil and provide nutrients to plants. Wheat is translocating less heavy metal to the edible part; it is, thus, the most suitable crop to be involved in the current context.

The objective of this study was to evaluate the effect of mixtures of the phosphate industry’s by-products and sewage sludge on some heavy metals (Pb, Zn and Cd) in the soil–plant system and the microbial load (bacteria, fungi and actinobacteria) in the soil. The experimental layout was a completely randomized design with ten treatments and four replications. The treatments consist of a combination of five substrates: phosphogypsum (PG), phosphate sludge (PS), sewage sludge (SS), phosphate waste rocks (PWR) and original mine topsoil (TS). Heavy metals analysis, phytoextraction efficiency (PEE) and bioconcentration factor (BCF) were carried out for three Ryegrass cuts. The microbial load of each treatment was determined at the end of the experiment. The results showed that the Pb, Zn and Cd contents of the treatments were well below the permissible limits given in the literature. The highest BCF and PEE were with treatment T4. Furthermore, bacteria, fungi and actinobacteria were significantly influenced by the different proportions of by-products used in the treatments, with the highest richness observed for the T4 treatment. For a successful reclamation of mine sites, it would be useful to determine the speciation of metals in the soil solution and the microbial genetic diversity.

Constructed wetlands offer sustainable, decentralized solution for wastewater treatment and reuse in Morocco. This study evaluates and compares four advanced vertical flow constructed wetlands (AVFCWs) incorporating locally sourced reactive media, to evaluate phosphate mining residues as a novel substrate. AVFCWs were designed with different substrate combinations, of pozzolan, phosphate mining residues (CW-B), clay (CW-C), and biochar (CW-D), alongside a control system (CW-A). The systems were operated under hydraulic retention times (HRTs) of 24, 48, and 72 hours corresponding to phase I, II and III respectively. Key water quality parameters in domestic wastewater were monitored, and evapotranspiration driven water losses were quantified. The results revealed that the use of reactive media significantly improved treatment efficiency, with CW-D achieving high removal efficiencies across most parameters. COD and TSS removal reached 80% and 88% respectively at 48h HRT, while nitrogen removal exceeded 82% in optimal configurations. CW-B achieved 76% phosphorus removal at 24h HRT, reaching 88% for CW-C at 72h. All AVFCWs exceeded 85% removal for heavy metals (Cu and Cd), with phosphate residues facilitating metal removal. On the other hand, faecal coliforms reached 3 Log reduction at an HRT of 24 h and decreased in subsequent phases, nevertheless exceeding Moroccan reuse limits. Extending hydraulic retention time improved the AVFCWs performance, but increased water loss (up to 28% at 72h) due to pronounced evapotranspiration in semi-arid to arid regions. Although all substrates demonstrated high performance, phosphate mining residues emerge as promising substrate pending further optimization, supporting circular economy objectives.

Constructed wetlands offer a sustainable, decentralized solution for wastewater treatment and reuse in Morocco. This study evaluated mesocosm-scale advanced vertical flow constructed wetlands (AVFCWs) incorporating locally sourced reactive media to assess phosphate mining residues as a novel substrate. Accordingly, four configurations were compared: a sand-based control (CW-A) and three amended systems combining pozzolan with phosphate mining residues (CW-B), clay (CW-C), and biochar (CW-D), operated in batch mode under hydraulic retention times (HRTs) of 24, 48, and 72 h. The incorporation of reactive media significantly improved treatment efficiency, with CW-D achieving high removal efficiencies across most parameters. COD and TSS removal reached 80% and 88%, respectively, while nitrogen removal exceeded 82% in optimal configurations. Phosphorus removal reached 76% in CW-B and 88% in CW-C. The removal of Cd and Cu exceeded 85% in all systems, with phosphate mining residues demonstrating strong potential for metal immobilization. However, despite these high removal efficiencies, the treated effluent did not meet Moroccan reuse standards for cadmium and fecal coliforms, indicating that single-stage AVFCWs are insufficient for safe agricultural reuse and require additional polishing steps. Extended HRT improved AVFCWs’ performance, but increased water loss, reaching up to 28% due to evapotranspiration. Hence, phosphate mining residues emerge as a promising substrate, pending further optimization, while supporting circular economy objectives.