*2.4. Treatment of Faecal Sludge*

In some developing countries still relying on pit latrines, filled up latrines are either closed or emptied and the sludge disposed off-site as waste [17]. Sludge can also be utilized as a soil ameliorant, for improving the soil status [61]. However, land application of sludge can also promote the pollution of water and soil by heavy metals [62]. Prior to sludge applications, conventional treatments are carried out [62], but that is not normally the case in most developing countries. The removal of heavy metal pollutants can be achieved through these conventional techniques to treat wastewater streams, including reduction or precipitation via chemical means, ion exchange, electro-chemical methods, and reverse osmosis. Nonetheless, such processes can be inadequate, especially for solutions with 1 to 100 (mg/L) of metal concentrations [63]. Other methods have also been successfully used for heavy metal removals, microbial remediation, and phytoremediation: cortex fruit wastes, including banana, kiwi, and tangerine peels [55]; activated carbon, peanut husk charcoal, fly ash, and natural zeolite [47]; composting and immobilization using biochar [64]. Such processes are cost effective, with non-hazardous end products [65]. The effective elimination of heavy metals from wastewater relies on several aspects, such as sludge concentration, the solubility of metal ions, pH, the metallic species and its concentration, and wastewater contamination load [63,66].
