Construction And Performance Optimization Of Worm Reactor For Waste Activated Sludge Reduction

With the growing of municipal wastewater amount and treating rate,the production of waste activated sludge(WAS)correspondingly rises.The WAS contains a large amount of water,refractory organic matters,heavy metals and pathogenic microorganisms,which will have a serious risk to the environment if discharging without treatment.Current WAS treatment technology mainly includes aerobic digestion,anaerobic digestion,hot drying,wet oxidation and so on.However,these sludge treatment technologies have some drawbacks such as high cost and serious secondary pollution.Recently,biological predation technology has attracted increasing attentions due to its advantages of low energy consumption,clean and pollution-free.Nevertheless,the bottlenecks of the biological predation process including unstable sludge reduction efficiency and difficult control of worm growth conditions have limited its application.In order to solve the above problems,a worm reactor suitable for worm growth was developed based on the survival mode of worms in natural environment and the characteristics of prey objects,and the sludge pretreatment technology was used to adjust the properties of WAS for promoting the worm predation behavior and enhancing the sludge reduction effect.In the meanwhile,forward osmosis(FO)technology was applied for treating the by-products of worm predation.The main research contents and results are summarized as follows:(1)The worm specie used in this study is Limnodrilus hoffmeisteri.Based on this worm,a worm reactor was developed,and its optimal operating conditions were obtained as follows:the temperature of the water chamber was 25±2℃,the dissolved oxygen of the water chamber was 4-6 mg/L,the worm attachment density was 3 kg·ww/m~2,and the operation was in intermittent mode(operation time:intermittent time of 2h:4h).Under the optimal operating conditions,the corresponding efficiency of worm feeding and worm recovery were 42.14%and68.52%,respectively.(2)The effects of ultrasonic treatment,low temperature heat treatment and chemical treatment on the properties of WAS and on sludge reduction of the worm reactor were investigated.Compared with low temperature heat treatment and chemical treatment,ultrasonic treatment had the most obvious effects on sludge properties and the best sludge reduction effect,and the corresponding worm predation efficiency and worm recovery rate reached 69.54%and98.20%,respectively.Based on the correlation analysis via data processing software(SPSS25.0),it was found that the worm predation efficiency and the worm recovery has a significant positive correlation with soluble microbial products(SMP)and sludge particle size but a significant negative correlation with bound extracellular polymers(BEPS)and sludge volume index(SVI).(3)The influence of ultrasonic time and ultrasonic output power on the ultrasonic pretreatment effect was investigated.The results indicated that when the ultrasonic output power and the ultrasonic time were 36 W and 20 min,respectively,the worm reactor had the best operation effect and the corresponding worm predation efficiency and worm recovery rate were 65.58%and 79.44%,respectively.The main prey of worms was tryptophan and tyrosine proteins in sludge BEPS.Compared with the initial sludge,the floc structure of the worm metabolites was more compact and the filamentous bacteria became less,which effectively improved the settling performance of the sludge.(4)The feasibility of simultaneous digestion and dewatering of worm metabolites by FO technology was explored.The results showed that after the combined treatment of pretreatment,worm reactor and FO reactor,the reduction efficiency of the WAS reached 55.83%,and the concentration of the concentrated sludge reached 35.12 g/L,and the sludge volume is reduced by 94.41%,At the same time,the effluent quality of the combined device could meet with the standards of"Municipal Sewage Recycling-Municipal Water Quality"(GB/T18920-2002).The developed combining technology of ultrasonic pretreatment,worm reactor and FO reactor can achieve not only the synchronous dewatering and digestion of the WAS but also the effluent water directly discharging or reusing,which provides a novel technology for WAS reduction and stabilization.