Recovery of biosolids from constructed wetlands used for faecal sludge dewatering in tropical regions.

Biosolids recovered from yard-scale vertical-flow constructed wetlands used for faecal sludge dewatering in Cameroon, were analyzed to assess their degree of maturity, nutrient and heavy metals contents, as well as their hygienic quality. Six beds were loaded weekly at nominal loading rate of 100, 200, and 300 kg TS/m2/year. The quality of the biosolids accumulated in the beds was monitored during 6 additional months of resting period prior to final harvest. Results showed that C/N ratio (11.3), humification index (14%), humification rate (1.8%), and degree of polymerization (3.7) of the biosolids generated were comparable to those of mature composts. Biosolids quality appeared to having high fertilizing value (N: 2%, P2O5: 2.3%, CaO: 1%, MgO: 0.14%, K2O: 0.03, and Na2O: 0.09%) with low heavy metals contamination (63, 14, 26, 2.4, 575, 703, 186, and 32 mg/kg for Pb, Ni, Cr, Cd, Cu, Zn, Mn, and Se, respectively). The concentration of fertile ascaris was reduced from 40 eggs/g TS after one month storage to <4 eggs/g TS after six month of storage, a level which does not significantly increase health risk exposure as compare to the WHO guidelines.