Removal Of Heavy Metals From Activated Sewage Sludge And Its Reutilization

With the features of high moisture content, large production and high organic mattercontent, anaerobic degradation and corruption can easily react in the sludge and producestench. And also, the sludge contains a variety of poisonous, harmful heavy matal materials,macromalecular organic matters that are difficult to degrade and large quantity ofdisease-causing organisms and parasite. If sludge cannot be treated properly, it must causedamage to the eco-environment and human beings.The main sludge treatment and disposal methods at home and abroad are landfill, landuse, incineration and casting off into the sea.These methods have some defects, such aslandfill has longer processing cycle and needs to take up a lot of land resources; the cost ofsludge incineration processing is higher, and treatment facilities investment also is higher; andthe land use will cause soil pollution, because sludge contains the disease-causing organisms,parasitic ovum and harmful heavy metals and so on, with rain runoff, those harmfulsubstances will go into the soil, etc. From the point of the utilization, sludge contains a lot oforganic matters, plant nutrients available (N, P, K, Zn, Ca, etc), the methods of the traditionalsludge treatment apparently ignored the potential value. In fact, through the appropriatemethod, the sludge can get effective utilization.In this paper, pretreated sludge firstly, its aim is to degrade macromolecule and refractoryorganics into small molecular organic matters and improve sludge characteristics, then sludgeused for breeding flies maggots after pretreatment. In breeding process, because ofbioconcentration, heavy metals removed further. After the process of breeding maggots, if theheavy metal content of treated sludge reached agricultural standard, treated sludge could beused as organic fertilizer.In this paper, pretreatment methods of sludge contain Fenton reagent pretreatment andanaerobic fermentation pretreatment. The results of experiments showed that, the optimumconditions by Fenton reagent were as follows: the dosage of hydrogen peroxide was3.5%, thedosage of acetic acid was3.5%, the dosage of ferrous sulphate heptahydrate was1%, thetemperature was95℃, the liquid-solid ratio was1:1and reaction time was45min, the rate ofsludge dewatering was67.5%, the removal rates of Zn, Ni, Cu, Cr and Pb were45.6%,42.9%,36.8%,28.6%and14.5%respectively, the smell of the sludge greatly abated, the quantity ofdrogen sulfide and ammonia released was low. And sludge anaerobic had an incompleteanaerobic fermentation process, the optimum conditions were that room temperature wasfrom25℃to30℃, the dosage of calcium carbonatewas1.2%and fermentation time was7d,under these conditions sludge made a good effect of breeding maggots. The sludge after Fenton reagent pretreatment bred maggots could achieve good results,the optimum conditions were that the moisture content of sludge was75%to80%, thetemperature was30to50degree celsius and the weight of the maggot eggs was5g/10kgoriginal sludge, the weight of maggots was1198g/10kg original sludge. And the heavy metalcontent of this treated sludge and the sludge after pretreatment by Fenton reagent could meetthe standard of NY (525-2002) and GB (4284-1984), which could be used as fertilizer.The sludge after anaerobic fermentation pretreatment bred maggots could achieve goodresults, the optimum conditions were that the moisture content of sludge was75%to80%, thetemperature was30to35degree celsius and the weight of the maggot eggs was6.5g/10kgoriginal sludge, the weight of maggots was1422g/10kg original sludge.