Demonstration Project Research On Sewage Sludge Anaerobic Fermentation For Acids Production Under High Loading Rate

In recent years,the technology of waste sludge anaerobic fermentation has received wide attention from scholars since it can produce volatile fatty acids?VFAs?with high added value.However,most of the studies are conducted under conditions of low feed load,and the low feed load will lead to large land occupation for equipment,high equipment investment costs,low treatment efficiency and low benefits.Therefore,increasing feed load is the key to the application of this technolo gy.Based on our previous research,a model project of sludge anaerobic fermentation with a treatment capacity of 2.1 m³ of sludge?85%moisture content?/day was established in a wastewater treatment plant in Wuxi C ity.The procedure characteristics and feasibility of high-load sludge anaerobic fermentation to produce VFAs were studied in this paper based on the sludge from the wastewater treatment plant.The main results of this paper are listed as follows:?1?A method for the start-up of sludge anaerobic fermentation for acid production was explored.The results showed that the multiple domestication and inoculation of seed sludge could enrich the acid-producing bacteria.The average total volatile fatty acids concentration reached 3.26 g/L and average ac id yield was 256.91 mg COD/g VSS during the semi-continuous and stable operation process of the project.At the same time,acetic acid,as the highest content of organic acids,the proportion was 52.45%.In the fermentation broth,SCOD reached 7587.79 mg/L,and in which VFAs accounted for 60.78%,and the degradation rates of TSS and VSS after fermentation were 23.64%and 44.41%respectively.At the same time,the removal rates of soluble proteins and polysaccharides reached 62.31%and 54.60%respectively.The start-up method used in this study not only realized the start of this sludge anaerobic fermentation project,but also enriched a large number of acid-producing bacteria.It is of great significance to the engineering application of sludge anaerobic fer mentation technology.?2?The impact of alkali type on sludge pretreatment and fermentation under demonstration project was investigated.The results indicated that NaOH had the highest efficiency in sludge hydrolysis,the average concentration of SCOD in pretreated sludge increased to 22,389.21 mg/L and the hydrolysis rate reached 64.26%.However,the content of the by-products?NH₄⁺-N?in pretreated sludge was higher,and the concentrations of TN and TP reached 1476.51 and 348.36 mg/L respectively.In add ition,calcium peroxide pretreatment could effectively improve the VFAs production and acid yield,specifically,the average concentration of total acid was 7.93 g/L and the acid yield was 273.93 mg COD/g VSS.Simultaneously,the ratio of acetic acid could reach 60.35%;the average TSS and VSS decreased by 24.42%and 47.62%respectively after fermentation.The calcium peroxide could effectively remove the NH₄⁺-N and orthophosphate in the fermentation broth while maintaining the stability of alkaline reactio n system.The average concentrations of NH4⁺-N and TP in the semi-continuous operation period were 286.33 and 17.42 mg/L respectively.The net profit of sludge anaerobic fermentation with mixed alkali,calcium peroxide and sodium hydroxide pretreatment was 229.14,257.37 and 10.49 yuan/t respectively.Hot-mixed alkali and hot calcium peroxide are economically feasible pretreatment methods for sludge anaerobic fermentation.?3?The effect of heat-alkali pretreatment on hydrolysis and fermentation performance of high solids-containing was studied.The results showed that the SCOD in the high solids-containing sludge increased by 8.17 times and the hydrolysis rate reached 56.82%after thermal alkali pretreatment,it meant that the thermal alkali pretreatment of high solids-containing sludge played an important role in improving the conversion efficiency of biomass energy and reducing the energy consumption during the entire process.Simultaneously,the fermentation of high solids-containing sludge would also lead to the accumulation of a large number of VFAs.During the semi-continuous and stable operation process,the average VFAs concentration in the fermentation broth was 8.39 g/L.And the ratio of acetic acid reached 62.10%.In addition,the average organic acid yield during semi-continuous operation process was 234.91 mg COD/g VSS.The residual sludge could be fully degraded after pretreatment and anaerobic fermentation,the degradation rates of TSS and VSS after fermentation were 28.70%and 48.21%respective ly.Otherwise,the removal rate of soluble proteins and polysaccharides reached 61.25%and 50.90%.The effective degradation of soluble proteins and polysaccharides indicated that the model project for sludge anaerobic fermentation operated well.?4?The effect of co-fermentation on the anaerobic fermentation of high-loading sludge under demonstration project was investigated.The results showed that adding kitchen waste in excess sludge was conducive to the rapidly dissolution of SCOD,and the hydrolysis rate reached 55.12%.At the same time,the addition of kitchen waste in the excess sludge for co-fermentation could also effectively increase the production and yield of VFAs.The average concentration of total acid was 13.62 g/L and the average acid yield was 379.31 mg COD/g VS.The content of acetic acid and butyric acid in the fermentation broth obtained from the co-fermented sludge was comparable and greater than that of other organic acids.In addition,SCOD reached 29576.04 mg/L in the semi-continuous fermentation period,and VFAs were the main components,accounting for 68.52%.The average concentrations of TN,TP and ammonia nitrogen in the fermentation broth reached 1865.18,22.04 and 385.06 mg/L.The addition of food and kitchen waste is conducive to the increase of acid production.At the same time,the content of VFAs in fermentation broth is also higher,and it is of better quality when used as a supplementary carbon source.The TS and VS degradation rates of the co-fermented mixed substrates reac hed 31.56%and 55.65%.At the same time,the addition of food waste was beneficial to increase the degradation rate of protein and polysaccharide in the substrate.The degradation rates of soluble protein and polysaccharide were 70.85%and75.58%,respectively.