外文原文-绕过原生废水厌氧消化和用IC-SBR法后续处理养猪废水.pdf

Short communication Anaerobic digestion and post treatment of swine wastewater using IC SBR process with bypass of raw wastewater Liang Wei Deng a b Ping Zhenga Zi Ai Chenb aDepartment of Environmental Engineering Zhejiang University Hangzhou China b Asia Pacifi c Regional Biogas Research and Training Center Chengdu China Received 14 May 2005 received in revised form 19 October 2005 accepted 20 October 2005 Abstract A combined system consisting of Internal Circulation IC anaerobic reactor and Sequencing Batch Reactor SBR was used to treat swine wastewaterinordertoestablishacost effi cientwastewatertreatmentsystem ICreactorcouldremoveabout80 ofCODwithorganicloadingrate of 6 7 kg COD m3day in treating raw swine wastewater Performance of direct post treatment of digested swinewastewater was very poor with COD removal 7 54 and NH3 N removal 81 2 because of the low biodegradability and improper carbon nitrogen ratio Performance of post treatment using SBR with the addition of raw wastewater was good with effl uent COD less than 300 mg L and effl uent NH3 N less than 10 mg L The removal rates of COD BOD5 NH3 N and TN were 95 5 99 6 99 4 and 94 3 respectively in the IC SBR system with total hydraulic retention time of 5 6 days 2005 Elsevier Ltd All rights reserved Keywords IC anaerobic reactor Sequencing Batch Reactor SBR Swine wastewater treatment Nitrogen removal 1 Introduction The swine wastewater is widely used as fertilizer in many countries because of its high organic nitrogen and phosphorus content If a large herd of pig is raised in a restricted area it is very diffi cult to landspread all the swine waste Moreover the swine waste possibly leads to local soil pollution and eutrophication of water body So many countries are paying attention to the pollution resulted from livestock farms and have tighten legislation and discharging standards As far as swine waste treatment is concerned anaerobic digestion is important alternative to land application because it reduces pollution and recovers methane A number of studies and applications have been reported for anaerobic digestion of swine waste 1 4 However because of the longer hydraulic retentiontime HRT andloworganicloadingrate largereactor volume and high investment are needed Internal Circulation IC reactor provides a promising way to solve the problem since it is an effi cient anaerobic reactor 5 6 The effl uent from anaerobic digestion contains high COD nitrogen and phosphorus concentration It is necessary to set up a post treatment to meet the discharge standards However previous studies showed that the effi ciency of direct post treatment was not satisfactory because of the poor biodegrad ability and low COD NH3 N ratio in effl uent 7 11 Thus new treatment strategy should be developed The objective of this study was to establish a cost effi cient treatmentsystemforswinewastewater andtotestthefeasibility of anaerobic digestion and post treatment using IC SBR process with bypass of raw wastewater 2 Material and method 2 1 Experimental system The IC SBR process is shown in Fig 1 2 1 1 IC reactor As shown in Fig 1 IC reactor was made of stainless steel with side length 320 mm height 1300 mm and total volume 133 L working volume 120 L Two gas liquid solid separators were located in the middle and upper parts of the reactor A gas collector was connected with the two separators and a distributor was installed on the reactor bottom The IC reactor was fed by pump model SP 950 and the effl uent was overfl owed from weir to water container It was seeded with 35 0 L anaerobic sludge obtained from a full scale digester treating swine wastewater and was fi lled with tap water and raw swine wastewater After 3 days settling period the IC reactor was fed with raw Process Biochemistry 41 2006 965 969 Corresponding author Tel 86 571 86971709 fax 86 571 86949320 E mail address pzheng P Zheng 1359 5113 see front matter 2005 Elsevier Ltd All rights reserved doi 10 1016 j procbio 2005 10 022 swine wastewater The effl uent from IC reactor was treated by SBR The temperature for the experiment was maintained at 20 25 8C 2 1 2 Sequencing Batch Reactor SBR SBR was also made of stainless steel with side length 320 mm height 320 mm and total volume 32 7 L working volume 18 L Air was supplied by aircompressor modelACO 001 andwasreleasedthroughastonediffuseron the bottom of SBR Fig 1 A mini pump model SP 1000 was used for FILL and DISCHARGE After SBR was inoculated with 5 0 L sludge cultivated in our laboratory the reactor was fi lled to fi nal volume with effl uent from IC reactor and was then operated at hydraulic retention time of 3 days and biological solid retention time SRT of 30 days The temperature was also maintained at 20 25 8C The sequencing scheme consisted of 3 h AERA TION 3 h IDLE 3 h AERATION 1 h SETTING 1 h DECANT and 1 h FILL FILL REACT SETTLE DECANT and IDLE were controlled by programmable timer Sludge was drawn by siphon manually No forced agitation was applied 2 2 Materials Swine wastewater for the study was obtained from a local pig farm It was allowedtosettlefor6 12 htoremovesomesuspendedsolids TheCOD BOD5 NH3 N and TN concentrations were 3000 15 000 mg L 1700 8500 mg L 400 1400 mg L and 600 2100 mg L respectively 2 3 Analytical methods Samples were taken to determine COD NH3 N and SV30every day and to monitor BOD5 SS TN and TP once a month Analysis of COD BOD5 SS NH3 N TN andTPwascarriedoutaccordingto thestandardmethodsissuedby the China National Environmental Protection Agency 12 3 Results and discussion 3 1 Performance of pretreatment with IC reactor At the beginning of experiment 40 L swine wastewater was fed into IC reactor each day and a hydraulic retention time of 3 days was controlled As shown in Fig 2 COD removal went up to 80 or higher within 2 weeks when the organic loading rate was 1 2 kg COD m3day Then the organic loading rate was increased by means of enhancing infl uent concentration or shortening hydraulic retention time In the end of experiment the 21st 22nd week the loading rate was 6 7 kg COD m3day the volumetric biogas production rate was about 3 m3 m3day and COD removal rate was about 80 It is L W Deng et al Process Biochemistry 41 2006 965 969966 Fig 1 Schematic diagram of IC SBR process Fig 2 Performance of IC reactor A loading rate and volumetric biogas production rate and B COD and NH3 N removal reported that the organic loading rate was 3 4 kg COD m3day and volumetric biogas production rate was 1 1 5 m3 m3day to treat the same wastewater with other kind of anaerobic reactors under similar conditions 1 3 13 14 Therefore IC reactor is very competent to treat swine wastewater It can be seen from Fig 2 that NH3 N concentration in effl uentwaslittlehigherthanthatininfl uent whichimpliesthat organic nitrogen was partly converted into ammonia nitrogen NH3 N during the pretreatment 3 2 Performance of direct post treatment with SBR SBR was operated to treat the effl uent from IC reactor directly After run for about 2 months the performance became very poor As listed in Table 1 the removal rates of COD and NH3 N were only 7 54 and 81 2 respectively The COD concentration 800 mg L andNH3 Nconcentration 100 mg L in SBR effl uent were high The results were similar to those observed by Su et al 11 They reported that COD removal ratewas only 10 4 43 6 and TKN removal was 42 5 71 1 when SBR was used to treat digested swine wastewater In order to fi nd out the reason of poor removal effi ciency of COD and NH3 N the characteristics of infl uent and effl uent of ICreactorwere analyzed Theratio ofBOD5 CODisoftenused as an index to evaluate biodegradability of wastewater BOD5 COD 0 45 indicates that biodegradability is very good BOD5 COD 0 3 0 45 biodegradabilityisgood BOD5 COD 0 2 0 3 biodegradability is poor BOD5 COD 0 2 biotreatment is unsuitable The ratio calculated from Table 2 indicated that the BOD5 COD ratio of raw swine wastewater IC infl uent was 0 66 and its biodegradability was very good After anaerobic pretreatment most of biodegradable organic pollutants in raw swine wastewater were degraded The BOD5 COD ratio of digested effl uent IC effl uent fell to 0 18 and its biodegradability became very poor The suitable ratio of carbon nitrogen and phosphorus for microbial growth is BOD5 N P 100 5 1 while the ratio of BOD5 N P of raw swine wastewater is about 20 4 4 6 1 calculated from Table 2 that means the raw swine wastewater was already maladjust ment for microorganism growth The BOD5 N P ratio of digested swine wastewater was changed into 3 1 10 2 1 that means the digested swine wastewater is seriously short of organic matter These factors would infl uence aerobic post treatment of digested swine wastewater pH in SBR dropped sharply during AERATION when NH3 N was oxidized In the end of the fi rst AERATION pH dropped to 6 0 or so In the stage of IDLE 3 6 h pH rose a little due to denitrifi cation In the end of the second AERATION 3 9 h pH fell below 5 5 which may inhibit thebacterial activity Thiswasreasonbehindverypoorremoval effi ciency of COD and NH3 N to treat IC reactor effl uent with SBR directly In the stage of FILL 11 12 h digested swine wastewater was fed and pH only went up to about 6 8 less than initial pH of the cycle The NOx N the sum of NO2 N and NO3 N at the end of cycle was higher than that at the beginning of cycle indicating accumulation of NOx N Fig 3 It could be attributed to feeble denitrifi cation because therewas not enough biodegradable organic substance in digested swine wastewater 9 Judged from above mentioned results the performance of conventional anaerobic aerobic process treating swine waste water is poor and its stability is unstable New strategy for post treatment of digested effl uent should be tried 3 3 Performance of post treatment using SBR with addition of raw wastewater In order to improve post treatment of digested swine wastewater raw swine wastewater was added into digested swine wastewater The ratio of raw wastewater to digested swine wastewater was about 1 2 As a result both the ratio of BOD5 COD and the proportion of BOD5 N P in SBR infl uent were increased The removal rate of COD and NH3 N arose largely As listed in Table 2 the COD less than 300 mg L and BOD5 less than 20 mg L in SBR effl uent were low and such low effl uent COD and BOD especially in digested swine wastewater treatment have been rarely reported so far The NH3 N removal was also very good in SBR treating digested swinewastewater with addition of rawwastewater The infl uent NH3 Nwasashighas1400 mg Lwithaverageconcentrationof 721 mg L while the effl uent NH3 N was lower than 10 mg L withremovalratemorethan99 Ithasbeenconfi rmed thatthe high NH3 N removal rate mainly resulted from biological nitrifi cation rather than air stripping 15 As shown in Fig 3 during AERATION about 70 mg L of NH3 N was converted into nitrite nitrate while pH value was always kept at higher than 7 0 in SBR treating digested swine L W Deng et al Process Biochemistry 41 2006 965 969967 Table 1 Performance of SBR treating digested effl uent of swine wastewater Parameters Infl uent mg L Effl uent mg L Removal rate COD955 281883 2897 54 NH3 N702 95 6132 48 881 2 Table 2 Overall removal effi ciencies of pollutants by IC SBR process Parameters Infl uent of IC Effl uent of IC Infl uent of SBR Effl uent of SBROverall removal COD mg L 6372 16391229 3972811 825288 59 295 5 BOD5 mg L 4210 353223 77 81293 33315 6 6 299 6 NH3 N mg L 707 162727 167721 1663 89 5 4899 4 TN mg L 918 164739 136793 14451 9 0 194 3 wastewater with addition of raw wastewater It indicated that the SBR system had a larger buffering capacity than the SBR for direct post treatment During AERATION 0 3 h and 6 9 h NOx N increased as NH3 N was oxidized During IDLE stage 4 6 h and 10 12 h however NOx N decreased due to denitrifi cation In SBR treating digested swine wastewater without addition of raw wastewater removed NOx N in denitrifi cation was less than that produced in nitrifi cation resulting in NOx N accumulation and alkalinity shortage In SBR treating digested swine wastewater with addition of raw wastewater removed NOx N in denitrifi cation was far more than that produced in nitrifi cation because there was greater biodegradable organic substance in mixed swine wastewater 9 resulting in more alkalinity production in denitrifi cation than that consumed in nitrifi cation As a result pH value 7 58 in the end of cycle was higher than initial pH 7 16 and the nitrifi cation rate was better 3 4 Performance of the IC SBR system The overall performance of the IC SBR system is shown in Table 2 The pollutants were effi ciently removed with COD removal 95 5 BOD5removal 99 6 NH3 N removal 99 4 and TN removal 94 3 respectively These para meters were better than those from anoxic aerobic SBR Ng 10 Edgerton et al 16 and Fernandes et al 18 or combined anaerobic aerobic SBR Bernet et al 17 or hydrolysis reactor and SBR Deng 15 The IC SBR system is also superior to the system only using anaerobic process or the system only using SBR If swine wastewater is treated only with anaerobic process the concentration of pollutants was so high that it cannot meet the discharge standard If using SBR treats raw swine wastewater directly it takes very long HRT about 9 16 days 17 19 and requires a large reactor Moreover it consumes a lot of energy The HRT of IC SBR system with bypass of raw wastewater is 5 6 days and has shown a great advantage 4 Conclusions TheIC SBRprocessfortreatmentofswinewastewaterswas tested followingconclusionscanbedrawnbasedonthepresent study IC reactor could remove about 80 of COD with organic loading rate of 6 7 kg COD m3day in treatment of raw swine wastewater while the concentration of NH3 N in effl uent was little higher than that in infl uent Performance of direct post treatment of digested swine wastewater was very poor because of the low biodegrad ability and improper carbon and nitrogen ratio It is not feasibletotreatswinewastewaterwithconventional anaerobic aerobic process Performance of post treatment using SBR with addition of raw wastewater was good The removal rate of COD BOD5 NH3 N and TN were 95 5 99 6 99 4 and 94 3 respectively in the IC SBR system Based on the experiment IC SBR process with bypass of raw wastewater is developed to treat swine wastewater In the new process the raw wastewater is divided into two parts i e one part about 70 was fed into anaerobic reactor while the other part about 30 was bypassed into SBR to mix with digested wastewater L W Deng et al Process Biochemistry 41 2006 965 969968 Fig 3 Variations of main parameters during a cycle in SBR treating digested effl uent before and after addition of raw wastewater Profi le of A pH and B NH3 N and NOx N NO2 N NO3 N Acknowledgments Ministry of Science and Technology China supported this study work fi nancially The chemical analysis work of Miss Chen Gemin is also greatly appreciated References 1 Van Velsen 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