Effects Of Earthworm Treatment On Bioavailability Of Cadmium, Lead And Nutrients In Sewage Sludge

Laboratory incubation and pot trail were conducted to investigate the effects ofearthworm treatment and composting on the bioavailability of cadmuium (Cd) and lead(Pb) in sewage sludge. The main conclusions were as follows:1. Effects of composting on contents of nutrients and fractions of Cd and Pb insewage sludgeDue to composting, concentrations of both total and available nitrogen (N)decreased, while total amounts of phosphorus (P) and potassium (K), and availableamounts of P and K increased; contents of Exc, Car, Fe-Mn of Cd and Pb reduced, andcontents of 0xi, Res of Cd and Pb increased. Sewage sludge composting improved theproportion of stability fractions of Cd and Pb.2. Effects of Cd and Pb on the growth of earthworms and earthworm accumulationof Cd and Pb in sewage sludgeLow levels of Cd(8.51 mg/kg, DW) or Pb(377.43 mg/kg, DW) presented in sewagesludge stimulated earthworm growth, but high levels of Cd(25.02 mg/kg, DW) orPb(1242.85 mg/kg, DW) were toxic to earthworms and inhibited their growth. Thepoisoning symptom of earthworms could be observed in the treatment with high level ofPb in sewage sludge. There were mass on body surface of earthworms. In complextreatment of Cd and Pb, Make double factors analysis of variance on contents of Cd andPb to rate of earthworm increase, f=0.77, p=0.3973, There was no evidencely synergisticeffect on growth of earthworms in different concentration of combined treatment of thisexperiment.Earthworms could concentrate Cd in low concentrations of Cd of sewage sludge,but in high concentrations of Cd of sewage sludge, it absorbed Cd only, it had noconcentration effect on Cd. In different concentrations of Cd and Pb of sewage sludge,absorption coefficient of earthworms to Pb was low to 1, Which show that earthwormsabsorbed lead only, but it had no concentration effect on lead.3. Effects of earthworm treatment on fertility and fractions of Cd and Pb in sewagesludgeEarthworm activities increased pH of sewage sludge, facilitated the decompositionof organic matter, and reduced the contents of total N, also increased the contents ofavailable N and available P in sewage sludge; but hadn't caused any effects on contents of total P, total K and available K.Earthworm treatment could decrease the amounts of Cd and Pb in exchangeablefraction, increased the contents of of Cd and Pb in carbon-hydroxide bound form, but hadno effects on contents of Fe-Mn Cd, Fe-Mn Pb, Oxi-Cd, Oxi-Pb, Res-Cd and Res-Pb.4. Effect of sewage sludge application on yield, quality of Chinese cabbage and soilIn pot trail, application of sludge compost and sewage sludge at 10 g/kg(DW) couldpromote Chinese cabbage production obviously. The highest Chinese cabbage productionwas 79.01 g/pot(FW), Which increased 124.4ï¼…compared to CK(35.21 g/pot, FW). Application ofsewage sludge by earthworm treatment could further raise the yield of Chinese cabbage,with greater increases occurred in higher Cd and Pb treatments, effects on increasing theyield of Chinese cabbage obviously. Application of sludge compost and sewage sludgecould also increase the nitrate contents of Chinese cabbage, The highest nitrate contentsof Chinese cabbage was 2192 mg/kg(FW), it was higher than CK(923 mg/kg, FW), but itdidn't result in excessive accumulation of nitrate in Chinese cabbage. Application ofsewage sludge by earthworm treatment could reduce the nitrate content in Chinesecabbage. Application of sludge compost and sewage sludge could reduce the contents ofCd in Chinese cabbage, but it had no significant effect on the contents of Cd in Chinesecabbage. The highest Cd contents of Chinese cabbage was 0.342 mg/kg(DW), but itdidn't result in excessive accumulation of Cd in Chinese cabbage. Application of sewagesludge by earthWorm treatment could further reduce the contents of Cd in Chinesecabbage. Application of sewage sludge and sludge compost increased Cd and Pbconcentrations in soils, with greater increases occurred in higher Cd and Pb treatments.Application of sludge treated by earthworms had no significant effects on soil Cd and Pbcontents, compared with treatment without earthworms.