Reduction Of Municipal Sludge In Sewage Sludge With Corbicula Fluminea

The massive sludge not only occupy vast area of land, but also contain harmfulcomponents, it has become a public hazard of urban environment sanitation.Minimizing the emission of excess sludge has become an issue of concern. Accordingto ecological theory, micro-metazoan Corbicula fluminea can be used directly to ingestand digest the sludge containing high moisture content to achieve the purpose of thereduction of sludge.In this paper, the sludge of4typical municipal sewage treatment plants inNanchang has systematically analysed and selected the representation sludge for theexperiment of Corbicula fluminea to reduce sludge. Effect and mechanism of thereduction as well as the transfer of heavy metals by the Corbicula fluminea on sludgewas discussed. The main conclusions are as follows:(1) The physical and chemical properties of the sludge in Nanchang city meet theagricultural requirements, but the moisture content of sludge is higher and theconcentration of Cd in winter season exceeded the standard values for the pollutantsin agricultural sludge A(CJ/T309—2009). Sludge is rich in nutrients, and nutrientscontent have a certain regularity change in season. The nutrients content in generalhigher in winter than in summer, in which the organic content has reached asignificant difference in season. Other nutrients content and heavy metalsconcentration in the sludge seasonal differences did not reach significant level.Between organic matter and other nutrients showed a certain correlation and betweentotal nitrogen and total potassium had a significant correlation. Cu and Zn in thesludge reached a very significant level, presents significant levels of Zn and Cd. Cu,Zn, Pb and Cd showed a positive correlation which suggest that between the twotoxic elements exist combined pollution. The Corbicula fluminea reduction sludgetest choose the sewage plant’s sludge with high organic matter content and high othernutrients content were high heavy metals concentration.(2) Used the high moisture content sludge of aeration tank in selection of sewageplant to fed Corbicula fluminea, Corbicula fluminea had different survival rates anddifferent abilities of COD removal under different stocking densities. Under thehighest survival rate of Corbicula fluminea has the stocking density about35.16kg/m3, in which Corbicula fluminea also has the best ability on COD removal. So the bestbreeding density is about35.16kg/m3. The heavy metals in sewage and sludge have acertain degree of damage for the mantle, foot, visceral organs of Corbicula fluminea.From the electron microscope scanning pictures show no significant difference inCorbicula fluminea’ organ under different breeding density of heavy metals damaged.Contrast images can see obvious difference of the Corbicula fluminea’surfaceultrastructure btween without the heavy metal pollution and after sewage sludgefeeding.(3) The sludge through the Corbicula fluminea digestive funtion has convertedinto Corbicula fluminea feces. The sludge organics removal efficiency is35.78%. After8hours, Corbicula fluminea on the removal of suspended solids in water was54.5%.Corbicula fluminea to effectively reduce the content of TN, TP in sewage sludge, andwith the extension of time, the removal efficiency showed a trend of increase. After10days, Corbicula fluminea on the removal rate of TN, TP were52.65%and53.16%.(4) The Corbicula fluminea has strong enrichment ability of Zn, Cu, Pb, Cd, Crand Ni, and six kinds of heavy metals in the body content of Corbicula fluminea varied.The highest concentrations are Zn and Cu, other elements contents are much lower.The Corbicula fluminea reduction sludge has a certain influence on the content ofsoluble heavy metals in sewage. The content of the soluble heavy metals Zn, Cugradually greater than the detection limit and the rise during the experiment behind inwater, while the other four elements of Pb, Cd, Cr and Ni were below the detectionlimits. The Corbicula fluminea reduced sludge has certain effect of the soluble heavymetal content in the sewage, also can increase the soluble heavy metals such as Zn, Cu,and Cd.