different types of solid wastes is needed. Some of the solid wastes containvaluable metals. Their recovery through microbial and otherassisted recovery technologies seems feasible. To improve theyield of metal obtained through bioleaching of solid waste,new microbial strains have to be identified that can withstandhigher concentrations of potentially toxic metals. Microbialcommunity composition using DNA and PCR techniquesof different bio-heap systems, stirred tank reactors, and acidmine drainage sites will enrich knowledge of the potential ofvarious autotrophs and heterotrophs. The dynamics of microbialpopulations are variable both spatially and temporallyin the bioprocessing system. There is a need to defineand understand the potential interactions among the componentsof microflora. For this purpose, strains that havebeen deliberately genetically modified or selected by mutationshould be considered. Their use could reduce the residencetime and simultaneously enhance the economy of theprocess. Most microbe-metal interactions that occur in solidwaste processes remain unclear concerning the exact physiologicalmechanism of the microbes. Therefore, rapid, accurateand simple techniques are needed to gain greater controlover microbial processes by plant operators. To date, biotechnologicalleaching is practiced in a small number of industrializedcountries, but has great potential in developingcountries. For the sustainable environmental protection,both developed and developing countries must adopt theemerging leaching biotechnology process.