Physicochemical characteristics of soils from three communities (Umualumaku, Umeze II and Eziama) in Imo State, Nigeria, receiving application of palm oil mill effluent (POME) were investigated. Results obtained indicated that the soil sample from Umualumaku sampling station had the highest pH (5.25), conductivity (30.35 μs/cm), nitrate (50.73 mg/l), phosphate (10.10 mg/l), iron (5660.00 mg/l) and cadmium (4.20 mg/l), compared to the soil samples of the other two sampling stations (Umueze II and Eziama). It was observed that the raised concentrations observed in all the parameters investigated in the three sampling stations compared to the control samples was indicative of the fact that the raw POME was capable of impacting the soil. These results thus showed that raw POME is able to improve soil fertility and growth performance of crops if controlled application is practiced.

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An investigation into the ability of four inorganic coagulants namely; alum (Al2(SO4)3.18H2O), ammonium aluminum sulphate (NH4Al(SO4)2.12H2O), ferrous sulphate (FeSO4) and ammonium ferrous sulphate (NH4)2Fe(SO4)2.6H2O) in clarifying wastewater was examined. Results obtained from conventional standard ‘jar-test’ experiments indicated that alum was the most effective coagulant since it reduced turbidity of the wastewater to 0.64 NTU at a contact time of 300 min. Ferrous sulphate was the least effective coagulant, reducing turbidity of the wastewater to 3.45 NTU only at 240 min contact time, but when the contact time of the experiment was increased from 240 to 300 min, re-coloration of the solution was observed indicating re-stabilization of suspended particles. These findings tend to support the claim that alum is a choice coagulant for wastewater clarification.

The removal of heavy metals (HMs) in sewage sludge (SS) is important since sludge is often disposed or applied on farmland to enhance soil fertility. The present study reviewed two conceptual approaches (chemical and biological leaching) of removing HMs present in SS. In the chemical leaching method, traditional acid treatment together with novel methods such as aeration, complexation and sequential extraction procedure have been reviewed extensively. Certain factors influence the removal of HMs in SS. These factors include; pH, leaching agent, redox potential, and contact time. Nitric acid (HNO3), hydrochloric acid (HCl), sulphuric acid (H2SO4), phosphoric acid (H3PO4), ethylenediamine tetraacetic acid (EDTA), as well as Thiobacillus thiooxidans and Thiobacillus ferrooxidans are the most widely studied leaching agents and substrates involved in the chemical and bioleaching processes. However, the bioleaching process has been proposed as a safe, efficient, economical, environmental friendly method to remove HMs in SS due to its simplicity, high yield of metal extraction, low acid consumption, and low sludge solids concentration. Nevertheless, the present review has noted that most researchers are of the opinion that more studies are needed in the bioleaching method in order to enhance its commercial attraction.

An investigation into the ability of four inorganic coagulants namely; alum (Al2(SO4)3.18H2O), ammonium aluminum sulphate (NH4Al(SO4)2.12H2O), ferrous sulphate (FeSO4) and ammonium ferrous sulphate (NH4)2Fe(SO4)2.6H2O) in clarifying wastewater was examined. Results obtained from conventional standard ‘jar-test’ experiments indicated that alum was the most effective coagulant since it reduced turbidity of the wastewater to 0.64 NTU at a contact time of 300 min. Ferrous sulphate was the least effective coagulant, reducing turbidity of the wastewater to 3.45 NTU only at 240 min contact time, but when the contact time of the experiment was increased from 240 to 300 min, re-coloration of the solution was observed indicating re-stabilization of suspended particles. These findings tend to support the claim that alum is a choice coagulant for wastewater clarification.