Enhancement Of Waste Activated Sludge Anaerobic Digestion By The Addition Of Lime Mud From Papermaking Process

With rapid development of society,excess sludge production has a sharp increase.The disposal methods of sewage sludge（SS）for harmlessness,reductions and resource utilization have become an important environment problem facing the world today.Sludge landfill,incineration,aerobic composting,anaerobic digestion are frequently employed disposed methods.Currently,anaerobic digestion has become one of important biological technologies adopted to dispose of SS at home and abroad.Due to the hard degradation of various organic matters in SS,the rate and degree of SS is the main reason to restrict the performance of anaerobic digestion.Lime mud,a solid waste,generated from the causticizing process in paper making process（Lime mud paper-making,LMP）,is composed of Ca CO3 and slight amounts of elements,such as Mg,Na,Fe and mineral fillers,which could promote hydrolysis of SS and keep stability of reaction.Anaerobic digestion of SS was enhanced by LMP in this paper to provide theoretical and technical reference and support for utilization of SS and LMP.In this paper,LMP was used to enhance the performance of SS anaerobic digestion in terms of anaerobic single-phase batch reaction.The paper mainly studied the influences of solid content,temperature,LMP/VS ratio and heat treatment on SS anaerobic digestion.During the study of enhancement of high-solids thermophilic（55℃）anaerobic digestion of SS by the addition of LMP,LMP could strongly enhanced the performance from SS.When the LMP concentration reached 5 g/L,the max cumulative CH₄ production obtained from 400 g SS was 3286 ml,CH₄ yield reached 96.04ml/VS,which was 1.95 times than that of control group,VS removal rate reached to 17.5%,but further LMP dosage（≥7.5g/L）the performance of anaerobic digestion would be inhibited.The result indicated that the process of anaerobic digestion from SS used as an additive is feasible.The solid content of SS was an important factor of anaerobic digestion,compared with the performance of high-solids thermophilic（55℃）anaerobic digestion of SS,low-solid content could improve the performance of anaerobic digestion.When the LMP concentration was 2.5 g/L,the max cumulative CH₄ production obtained from 400 g SS was 4450 ml,CH₄ yield reached 155.4ml/VS,VS removal rate reached 30.5%,COD removal rate reached 84.6%.With LMP concentration increasing,the concentrations of NH₄⁺-N decreased at first and then increased,the concentrations of NH₄⁺-N in control reach 1386 mg/L,which was higher than 700 mg/L,ammonia inhibition was emerged at the control group.When the concentration reached over 2.5 g/L,the performance of anaerobic digestion would be inhibited.Compared with the results of previous chapter,the max CH₄ yield increased by 28.5%.Compared with thermophilic anaerobic digestion,the result of mesophilic digestion was lower than that of thermophilic anaerobic digestion,but stability of anaerobic digestion was better than that.When the LMP concentration was 2.0 g/L,the max CH₄ yield reached 153.2ml/VS,VS removal rate reached 28.04%,COD removal rate reached 68%.But further LMP dosage（≥2 g/L）the performance of anaerobic digestion would be inhibited.The performance of SS anaerobic digestion would be inhibited by LMP/VS ratio According to the comparisons of different LMP/VS ratio,the results demonstrated the best LMP/VS ratio of thermophilic（55℃）anaerobic digestion of SS was 1:16.Under the dosing ratio,CH₄ yield reached 161.2ml/VS,VS removal rate reached 32.1%.Heat pretreatment could promote the hydrolysis of SS obviously.The COD of digestion system could be rose with SS pretreatment（80℃ 120min）by heating alkali（LMP）,the value of COD reached 3180,3840,4280,4580 and 5740 mg/L respectively.The experimental group with initial p H=8.5,its CH₄ yield reached 165.45 ml/VS,much higher than that of the control group,CH₄ yield increased by 118%.The pretreatment could shorten the digest time;the digest time of batch experiment was 16 days comparing with 20 days of other conditions,the digest time had been shortened by 4 days.