Study On Sludge Dewatering Performance And Composting By Ultrasonic Wave Combined With Typical Adsorbents

With the process of urbanization and the increase of urban population,the corresponding sewage production and urban sludge production are also increasing.Many policies and documents have made clear the importance of sludge treatment and disposal."Urban Drainage and Sewage Treatment Regulations"has made requirements for sludge treatment:the government should support and encourage the treatment and disposal of sludge.“Action Plan for Prevention and Control of Water Pollution”（“Ten Principals of Water”）clearly points out:the innocent treatment rate of sludge in Chinese mainland should reach 90%above through 2020.High moisture content of sludge is an unavoidable problem when sludge is harmless and recycled,so it is very necessary to improve sludge dewatering performance before sludge recycling.The effects of adsorbent and ultrasonic on sludge dewatering performance were studied,and the combined treatment effect of the two technologies was also explored.Sludge conditioning experiments were carried out on five typical adsorbents selected by measuring the specific resistance to filtration（SRF）and capillary suction time（CST）.The results showed that the adsorbent could improve the sludge dewatering performance positively under certain conditions.The optimal dosage（mass fraction）of silica gel,zeolite,neutral alumina and activated carbon were 0.5%,0.3%,0.4%and 0.2%,respectively,and the polyacrylamide was 20 mg/L.At the same time,the five adsorbents were compared and analyzed,and it was found that zeolite was the best adsorbent in terms of treatment effect and economy,which could reduce the CST and SBF parameters of raw sludge from 67.40 s and 4.86×10¹³ m/kg to 54.21 s and 3.46×10¹³ m/kg,and the sludge conditioning cost was only 0.033 yuan per kg.The results of ultrasonic sludge conditioning experiment showed that appropriate ultrasonic parameters could also improve the sludge dewatering performance.When the ultrasonic frequency is 20 k Hz,the ultrasonic power is 20 W and the ultrasonic time is 5 s,the treatment effect is the optimal.The influence degree of ultrasonic factors on sludge conditioning effect was analyzed and studied.It was found that frequency had the greatest influence on sludge conditioning effect,followed by power and ultrasonic time.The combined treatment of zeolite and ultrasonic showed that ultrasonic combined with adsorbent treatment could further improve the sludge dewatering performance,and from the experimental results,the effect of zeolite first followed by ultrasonic treatment was better.At the same time,it was found that the three treatment methods of adsorbent conditioning alone,ultrasonic conditioning alone,and adsorbent combined with ultrasonic conditioning all made part of LB-EPS in sludge converted to SMP.The conversion ratio of the three conditioning technologies was the highest in combined conditioning,followed by zeolite conditioning,and single ultrasonic conditioning.Combined with the dewatering performance experiment,it was found that this conversion was beneficial to improve the dewatering performance of sludge,and SMP was easier to dehydrate than BEPS.This study also explored the effects of adsorbent conditioning alone,ultrasonic conditioning alone,and adsorbent combined with ultrasonic conditioning on subsequent sludge aerobic composting.By studying the change rules of temperature,p H,moisture content,organic matter,total nitrogen（TN）,total phosphorus（TP）,total potassium（TK）,total organic carbon（TOC）,C/N ratio,heavy metal content and seed germination index in the process of composting,it was found that all the three treatment programs could be composted normally,and the composting products with acceptable toxicity and successful maturation were obtained.Moreover,the analysis showed that the organic matter,TOC and water content of materials could be reduced faster by the combined conditioning.The organic matter decreased by 26.27%from 75.90%to 49.62%,with the largest rate of 0.88%/d.Moreover,the seed germination index（GI）of the combined conditioning group was 94.19%,higher than that of the single conditioning group and the original mud group.The removal rates of heavy metals（Pb,Cd,Cr,Hg,Cu,Zn,Ni,Fe）can reach 43.27%,47.84%,47.68%,66.97%,37.14%,59.84%,50.72%,45.65%,respectively.The content of heavy metals in the compost products meet the national standards for sludge land use.The results show that zeolite combined with ultrasonic sludge conditioning technology can promote sludge aerobic composting ripening,speed up the composting process,shorten the composting cycle and make the composting products non-toxic.