Disposal of water treatment wastes containing arsenic - a review.

Solid waste management in developing countries is often unsustainable, relying on uncontrolled disposal in waste dumps. Particular problems arise from the disposal of treatment residues generated by removing arsenic (As) from drinking water because As can be highly mobile and has the potential to leach back to ground and surface waters. This paper reviews the disposal of water treatment wastes containing As, with a particular emphasis on stabilisation/solidification (S/S) technologies which are currently used to treat industrial wastes containing As. These have been assessed for their appropriateness for treating As containing water treatment wastes. Portland cement/lime mixes are expected (at least in part) to be appropriate for wastes from sorptive filters, but may not be appropriate for precipitative sludges, because ferric flocs often used to sorb As can retard cement hydration. Brine resulting from the regeneration of activated alumina filters is likely to accelerate cement hydration. Portland cement can immobilize soluble arsenites and has been successfully used to stabilise As-rich sludges and it may also be suitable for treating sludges generated from precipitative removal units. Oxidation of As(III) to As(V) and the formation of calcium-arsenic compounds are important immobilisation mechanisms for As in cements. Geopolymers are alternative binder systems that are effective for treating wastes rich in alumina and metal hydroxides and may have potential for As wastes generated using activated alumina. The long-term stability of cemented, arsenic-bearing wastes is however uncertain, as like many cements, they are susceptible to carbonation effects which may result in the subsequent re-release of As.