Study On Effects Of Inorganic Salts On Forms Of Cu And Cd During Municipal Sewage Sludge Composting

Sludge is the inevitable product of the sewage treatment plant, industrial development and rapid progress of urbanization, exacerbated product of urban sewage sludge. From the beginning of the 1980s, the proportion of composting process increased year by year, which has becoming a mainstream way to solve municipal Sludge. A test was made to evaluate the changes of heavy metal (Cu, Cd) chemical speciation in composting with inorganic salts, such as ammonium carbonate, sodium silicate and ferrous ammonium sulfate. Summarized the influence of inorganic salts on heavy metals in sewage sludge compost, expect to explore the way to reduce the bioavailability.Test results are as follows:a variety of physical and chemical properties are in line with the basic conditions for agricultural sludge compost. Such as:pH 7-9, moisture content from 64% reduced to 40%, the conductivity of 4010.2 μm·cm-1. Total municipal sludge Cu is up to 413.3 mg/kg, Cd is up to 5.480 mg/kg. For Cu, exchangeable accounts for 16.65%, for Cd, exchangeable accounts for 26.89%, have a great bioavailability. During the composting process, morphological fractions have changed, exchangeable decreased most significantly, the effect of passivation is 97.07% and 78.48%. Adding 0.1% ammonium carbonate and 0.1% sodium silicate achieved good passivation results for Cu, and composting rate improved, passivation effect is weak with 0.1% ferrous ammonium sulfate.0.1% sodium silicate on Cd played a good passivation effect, increasing the amount of sodium is more effective. Composting rate has improved significantly with ammonium carbonate and ferrous sulfate. Adding inorganic passivating agents make the Cu and Cd accelerate the degradation rate, reduce bioavailability.