Experiment Study On Flocculation And Sedimentation Of Excess Sludge And Coal-washing Wastewater In Microwave Field

The excess sludge of municipal sewage treatment plant has the characteristics of high content organic compounds,thin grain, high rate of aquifer, difficult to sedimentation and dehydration. The coal-washing wastewater has lots of grains, high concentration of suspended substance and turbidity, the surface has minus charge, the grains was steady and difficult to subside.At present, the excess sludge and coal-washing wastewater are almost disposeed by flocculation and sedimentation,but that need large dosage of flocculant and high cost of flocculant.In this experiment, we combined microwave technology with flocculation technology to deal with excess sludge and coal-washing wastewater,reduced the dosage and cost of flocculant,. The experiment obtained the ideal intentions.The experiment investigated the effects of solo-Al₂(SO₄)₃ and PAC on excess sludge and coal-washing wastewater, and confirmed the best dosage of flocculant, It also researched the affects of microwave irradiation time,microwave power,pH value, confirmed the best combination of all factors. The experiment also investigated dehydration performance of sludge,turbidity of filtrate,moisture content,turbidity of coal-washing wastewater and Zeta potential, discussed the mechanism of flocculation and sedimentation, and in the last,discussed the mechanism of microwave and flocculation on excess sludge and coal-washing wastewater.the result of experiment indicated:(1) When used Al₂(SO₄)₃ to treat excess sludge and coal-washing wastewater, the best dosage of solo-agent was 1.25g/L and 1.188g/L, and when used combinatorial technique of microwave and flocculation, we can reduce the dosage of flocculant to 0.50g/L and 0.375g/L.(2) When used PAC to treat excess sludge and coal-washing wastewater,the best dosage of solo-agent was 0.50g/L, and when used combinatorial technique of microwave and flocculation, we can reduce the dosage of flocculant to 0.10g/L and 0.20g/L.(3)The Zeta potential of coal-washing was -9.23mV,the Zeta potential was augmented when the dosage of flocculant was increased. When reached isoelectric point,the dosage of PAC was 0.50 g/L, the dosage of Al₂(SO₄)₃ was 0.65 g/L.(4) The sedimentation speed of floc was related withρ_s,ρ_L,the diameter offloc,viscosity of liquid,when increased the density of grain, increased the diameter of floc, minished the viscosity of liquid, the sedimentation rate of floc can be enhanced.(5)When treated excess sludge and coal-washing wastewater with combinatorial technique of microwave and flocculation, the thermal effects and non-thermal effects of microwave played the adequate roles respectively.(6)Microwave irradiation can increase the speed of grain, the amount of grains neted by flocculant and the diameter of flocs, all of these were propitious to sedimentation of flocs.(7)Microwave has efficient thermal effects,the removeal efficiency of coal-washing wastwater with combinatorial technique of common calefaction and flocculation was worse than combinatorial technique of microwave calefaction and flocculation. Fit microwave irradiation can increase the speed of grain, reduce the stability of sludge, ameliorate the performance of sedimentation and dehydration,but excessive microwave irradialization can cause the destroy of cytoarchitecture of microbe, bring on the overflow of substance in the cell, increase the viscosity, deteriorate the performance of sedimentation and dehydration.(8)When treated excess sludge with combinatorial technique of microwave and flocculation,the biodegradability of supernatant of sludge was enhanced, so was easy for follow-up treatment.The combinatorial technique of microwave and flocculation is fire-new waste water treatment technics, and there is no report in the literature at home and abroad,the technics exert the characteristic of microwave sufficiently, reduce the dosage and cost of flocculant, so it possess high theoretical value and practical significance, when commence pilot study in the future, the operability and economicly of the technics should be considered.the sludge in the experiment was the excess sludge of urban sewage treatment plant, so the applicability of the technics on excess sludge of non-domestic sewage should be researched further more.