Waste revenue.

The recovery of metals from waste water can potentially generate revenue to offset water treatment costs. Solvent extraction/electrowinning is only employed for streams with very large mass loadings of recoverable metals, due to its high capital and operating costs and low efficiency at low metal concentrations. Electrometals/electrowinning (EMEW) which allows direct electrowinning without solvent extraction, employs a pair of tubular rather than planar electrodes in which the outer cathode and centrally placed anode are capped to form a cylinder through which the solution is pumped. The waste stream produced contains residual dissolved metal that requires treatment, and other limitations are that not all metals can be efficiently won, the presence of certain metals such as Fe can reduce current efficiency and increase operating costs, and the current density is relatively low. Lime treatment is easy to engineer and simple to operate and is cost-effective for treating large volumes of waste water which are not subject to strict discharge limits. It is also effective where the main contaminants are dissolved Al or Fe as the sludge formed is non-toxic, but for sites with heavy metals sludge management is a significant long-term environmental and financial liability. Reverse osmosis can be used to meet strict water quality criteria but is more costly and inefficient and produces a liquid brine stream that requires special handling. Reverse osmosis/membrane systems are best for sites with very low dissolved metal concentrations, but they also tend to result in more acidic water which may be harmful to the environment, so that neutralisation is required before discharge or re-use. Ion exchange is particularly effective where metal concentrations are low but still exceed discharge limits. Sulphide precipitation systems such as BioSulphide and Chemsulphide can be used to precipitate metals selectively and can treat large flows of water containing relatively low concentrati
The recovery of metals from waste water can potentially generate revenue to offset water treatment costs. Solvent extraction/electrowinning is only employed for streams with very large mass loadings of recoverable metals, due to its high capital and operating costs and low efficiency at low metal concentrations. Electrometals/electrowinning (EMEW) which allows direct electrowinning without solvent extraction, employs a pair of tubular rather than planar electrodes in which the outer cathode and centrally placed anode are capped to form a cylinder through which the solution is pumped. The waste stream produced contains residual dissolved metal that requires treatment, and other limitations are that not all metals can be efficiently won, the presence of certain metals such as Fe can reduce current efficiency and increase operating costs, and the current density is relatively low. Lime treatment is easy to engineer and simple to operate and is cost-effective for treating large volumes of waste water which are not subject to strict discharge limits. It is also effective where the main contaminants are dissolved Al or Fe as the sludge formed is non-toxic, but for sites with heavy metals sludge management is a significant long-term environmental and financial liability. Reverse osmosis can be used to meet strict water quality criteria but is more costly and inefficient and produces a liquid brine stream that requires special handling. Reverse osmosis/membrane systems are best for sites with very low dissolved metal concentrations, but they also tend to result in more acidic water which may be harmful to the environment, so that neutralisation is required before discharge or re-use. Ion exchange is particularly effective where metal concentrations are low but still exceed discharge limits. Sulphide precipitation systems such as BioSulphide and Chemsulphide can be used to precipitate metals selectively and can treat large flows of water containing relatively low concentrati