Fecal sludge treatment in a pilot-scale vertical-flow constructed wetland for the removal of helminth eggs

Abstract

Eliminating parasites in fecal sludge (FS) remains one of the major concerns in developing countries. To address this issue, experiments were conducted in triplicate vertical-flow constructed wetland (VFCW) units corresponding to free flow, 7 days and 14 days of retention time (RT). The effect of plant density on the system's performance was monitored in each planted bed unit and compared to the non-planted unit (standard). Following a bi-monthly application rate of FS at a nominal load of 200 kg TS m−2 year−1, the performance of the system in terms of helminth egg removal was calculated for each hydraulic RT tested. Untreated FS applied on the bed units contained high parasitic egg loads with a median number of 62.51 helminth eggs/g. The removal efficiencies of helminth eggs ranged from 82 to 100% in the leachates and were affected by the hydraulic RTs and the presence of plants (p < 0.05). On the other hand, accumulated biosolids on the bed units still contained high concentrations of pathogens exceeding the WHO standards and should not be applied directly in agriculture. HIGHLIGHTS The helminth egg analysis of the untreated fecal sludge revealed high concentrations with seven main species identified.; Fecal sludge treatment using the VFCW unit was not efficient enough to remove all helminth egg species.; The presence of plants and increase in retention times were found to positively affect the removal of helminth eggs in FS (p < 0.05).;

Keywords

• environmental pollution
• fecal sludge
• pathogenic parasites
• public health
• tropical climate
• vertical-flow constructed wetlands