26:T464,

A tubular membrane (MWCO = 200 k, PVDF, negative surface charge) and a hollow-fiber (HF) membrane (MWCO = 500 k, PS, neutral surface charge) underwent testing to determine their effectiveness in treating a sterilized wastewater from a dental clinic. The tubular membrane, which had a lower MWCO, produced a higher permeate flux due to the increased turbulence at the membrane surface that was possible with the tubular configuration (Reynolds numbers for the tubular module were over five times greater than the HF module). Both membranes had similar Hg rejections (tubular - 97%, HF - 98%) and permeate Hg concentrations (≤10 μg/L) due to particle size distribution of dental wastewater - the vast majority of the amalgam particles were larger than the pore size of either membrane. Permeate Hg was not a function of temperature, feed concentration, and intermittent operation. Because of their unique behavior and characteristics, both the HF and tubular modules will be tested at an actual dental clinic using non-sterilized dental wastewater.

27:T506,

Municipal and industrial wastewater treatment plants produce large amounts of sludge, mostly mechanically dewatered to approx. 25% DS and containing organic and mineral components. This sludge needs to be evacuated. Possible reductions of the amount of sludge produced are, hence, important. This paper describes the experimental results of peroxidation of thickened sludge (6% DS content). It can be concluded that peroxidation is efficient in reducing the residual sludge amounts. The optimum conditions correspond with adding 0.037 g H₂O₂/100 mL sludge at pH = 3 and in the presence of Fe²⁺ ions (1 mg Fe²⁺/100 mL sludge). Under these conditions, the rate of mechanical dewatering is significantly improved, and the amount of DS to be dewatered is reduced to approx. 80% of the initial untreated amount. Peroxidation preferentially releases ODS into the water phase. The slightly increased BOD/COD ratio converts this water phase into a more biodegradable and accessible carbon source for nitrification/denitrification. Heavy metals are also released in the water phase, and can be subsequently precipitated, thus reducing the residual heavy metal concentration in the residual DS.

28:T8ad,