Excess Sludge High Temperature - Temperature Two-phase Anaerobic Digestion Pilot Study

Along with the require of our national laws to the treatment and disposal of dirty water and sludge be raising continuously, the dirty water treatment plant is compelled to adopt series of improved measure, such as enhanced biological nitrient removal technology, extended aeration process, cancel primary setting tank etc. The sludge from the new process is hard to adopt traditional mesophilic anaerobic digestion.In order to solve the technical limit for traditional anaerobic digestion, the contrast research was carried out between the themophilic(55℃) and mesophilic (35℃) temperature co-phase anaerobic digestion(TPAD) and traditional single mesophilic anaerobic digestion(SMAD).The testing installation about TPAD and SMAD was built up, used the sludge production of typical model 100,000 tons/day municipal sewage plant reducing to 1/10,000 as design basis,and excess sludge of secondary tank for particular research object.The fermentation type and kinetic model of excess sludge in themophilic cidogenic phase was investigated.The results of the study were as follows: firstly, the pH value of themophilic phase and mesophilic phase of TPAD stabilized at 6.3-6.7 and 6.7-7.1 respectively, but the SMAD stabilized at 6.9-7.3;secondly, the total organic acids of mesophilic phase in TPAD were between the 420-680 mg/L,while in SMAD the total organic acids were between the 300-420 mg/L, accordingly, the propionic acid of themophilic and mesophilic phase in TPAD was between the 100-500 mg/L and between the 20-160 mg/L respectively, while in SMAD was between the 16-60 mg/L;thirdly, the ratio of organic acid to alkalinity in mesophilic phase of TPAD fluctuated between 0.25-0.4, as well as 0.1—0.2 of SMAD; fourthly, the reduction of volatile solids from TPAD was stabilized at 40-41%, Whereas the reduction of volatile solids from SMAD was less than 40%,but fluctuated between 37-39%;fifthly,the specific methane yield of TPAD was 460-500mLCH₄ /g VS_removed, while 430-450 of SMAD;sixth,the destruction of fecal coliform of TPAD fluctuated stably between 85-94%, Whereas the destruction of fecal coliform of SMAD fluctuated unstably between 25-60%. The fermentation type in themophilic cidogenic phase was investigated, the results were as follows:firstly, regardless whether the SRT of themophilic phase changed,the acetic acid was main acid,when SRT was 2.5days,the specific value of acetic acid/propionic acid/butyric acid was 5.2:2:1, when SRT was 1.2days,the specific value of acetic acid/propionic acid/butyric acid was 6.57:0.79:1;the alcohol had never checked out in the analytical test any time; The volume content of H₂ in biogas was always on 10^-4 scale.The results of the study proved that TPAD run steadily less than SMAD but put up a better processing ability under the condition of 15.5d sludge retention time of TPAD but 30d sludge retention time of SMAD,the reduction of volatile solids in TPAD is more than 40%, Can achieve the criterion of GB18918-2002;When using excess sludge as substrates of TPAD, the themophilic phase of TPAD don't come into being typical fermentative types such as ethanol-type fermentation, propionic acid type fermentation and butyric acid type fermentation; themophilic adification of TPAD system follows the Lawrence-McCarty kinetic model,and get correctional kinetic parameters: Y =0.14(mg Germs/mg VS_removed), K_d = 0.21d^-1,μ_max=1.44d^-1, K_s=11455.9mg/(L.VS).