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目 錄 1 引言 2 2 材料與方法 3 2．1 反應(yīng)器系統(tǒng) 3 2．2 分析方法 3 3 結(jié)果與討論 5 3．1 無(wú)過(guò)濾啤酒廢水組成 5 3．2 UASB反應(yīng)器的性能 6 4 結(jié)論 10 1. Introduction 12 2. Materials and methods 14 2.1. The reactor system used 14 2.2. Analytical methods 14 3. Results and discussion 16 3.1. Opaque beer brewery effluent composition 16 3.2. Performance of the UASB clarigester 17 4. Conclusion 22 References 23 24 熱帶氣候下UASB反應(yīng)器處理 無(wú)過(guò)濾啤酒廢水的研究 W. Parawiraa, I. Kuditab, M. G. Nyandorohb and R. Zvauyaa 摘要 對(duì)生產(chǎn)性UASB反應(yīng)器處理無(wú)過(guò)濾啤酒廢水的研究已進(jìn)行了兩年。該反應(yīng)器體積為500m3， 水停留時(shí)間約為24h。研究目的是根據(jù)處理效率評(píng)估UASB處理無(wú)過(guò)濾啤酒廢水的性能。未經(jīng)處理的無(wú)過(guò)濾啤酒廢水中懸浮物較多、有機(jī)物濃度較高，在排入城市污水處理廠之前必須進(jìn)行預(yù)處理。UASB反應(yīng)器COD平均去除率為57％ ，總固體和可沉降固體的去除率分別為50％ 和90％。由于UASB反應(yīng)器能積累氮、磷營(yíng)養(yǎng)物，因而出水的氮、磷含量高于進(jìn)水。研究結(jié)果表明，室溫下采用UASB反應(yīng)器處理無(wú)過(guò)濾啤酒廢水，出水能達(dá)到污水排放標(biāo)準(zhǔn)。 關(guān)鍵詞： 厭氧消化，UASB ，無(wú)過(guò)濾啤酒廢水，COD(化學(xué)需氧量) 1 引言 啤酒廢水常用好氧法和厭氧法來(lái)處理。Zvauya等人采用中溫好氧處理工藝處理無(wú)過(guò)濾啤酒廢水。由于啤酒廢水屬于中高濃度有機(jī)廢水，需要大量曝氣。同時(shí)，好氧法也會(huì)產(chǎn)生大量的剩余污泥，需要另外處置，這就相應(yīng)增加了污水處理的成本。Auster-mann-Haun和Seyfried采用UASB系統(tǒng)處理啤酒廢水，結(jié)果比好氧處理系統(tǒng)更加環(huán)保和高效。厭氧法具有以下幾個(gè)顯著優(yōu)點(diǎn)：無(wú)需曝氣，能耗較低；部分有機(jī)物轉(zhuǎn)化為甲烷，可作為能源；剩余污泥產(chǎn)量較少，處置費(fèi)用較低。有機(jī)污染物在大量厭氧微生物菌群共同作用下降解，其過(guò)程分為四個(gè)階段：水解、酸化、產(chǎn)乙酸和產(chǎn)甲烷階段。這些厭氧微生物，包括酸化菌、產(chǎn)乙酸菌和甲烷菌組成互養(yǎng)關(guān)系。近年來(lái)，由于啤酒廢水的特性適合厭氧法，因此廣泛應(yīng)用于啤酒廢水處理中。然而，厭氧法也存在著一些問(wèn)題：①厭氧反應(yīng)器初次啟動(dòng)過(guò)程緩慢；② 因?yàn)閰捬踹^(guò)程是由大量不同類屬的、相互制約的微生物菌群共同作用，厭氧處理過(guò)程不太穩(wěn)定，難于控制。啤酒廢水水質(zhì)復(fù)雜、波動(dòng)較大，而厭氧處理對(duì)水質(zhì)波動(dòng)尤為敏感。與生活污水相比，許多低pH、高有機(jī)負(fù)荷的工業(yè)廢水采用厭氧法尚有疑問(wèn)。但只要操作正確、監(jiān)控得當(dāng)，UASB反應(yīng)器運(yùn)行仍比較可靠。UASB污水處理系統(tǒng)運(yùn)行的可靠性依賴于設(shè)計(jì)人員提供可靠的控制程序和操作人員的全面監(jiān)控，盡量避免系統(tǒng)過(guò)負(fù)荷。雖然非洲國(guó)家大多數(shù)無(wú)過(guò)濾啤酒企業(yè)都屬于大型企業(yè)，但很少有幾家企業(yè)愿意處理其廢水。本研究采用哈拉雷市最大的無(wú)過(guò)濾啤酒廠Zimbabwe新安裝的UASB反應(yīng)器，來(lái)評(píng)估其處理效果。 2 材料與方法 2．1 反應(yīng)器系統(tǒng) 該反應(yīng)器材質(zhì)為混凝土，體積為500m3，平均有機(jī)負(fù)荷為6kgCOD／(m3·d)。該廠污水處理系統(tǒng)包括集水池、篩濾(孔徑0．5mm)、均衡池和UASB反應(yīng)器。篩濾除去廢水中大的懸浮物。均衡池用于均勻有機(jī)負(fù)荷、pH和啤酒間歇生產(chǎn)造成的水質(zhì)波動(dòng)，同時(shí)也稀釋釀造過(guò)程中產(chǎn)生的有毒和抑制性化合物的濃度。在均衡池內(nèi)投加尿素和正磷酸鹽，以補(bǔ)充氮和磷等營(yíng)養(yǎng)元素，保持廢水中COD：N：P的比例為100：5：1。若廢水呈酸性(pH=3．3～6．3)，則加堿調(diào)節(jié)進(jìn)水DH值至中性。均衡池出水進(jìn)入U(xiǎn)ASB反應(yīng)器的底部，然后與氣體一起從反應(yīng)器頂部流出。在37±2℃ 的溫度范圍內(nèi)，UASB反應(yīng)器采用活性污泥接種。污泥的培養(yǎng)馴化期為3個(gè)月，其間采用間歇進(jìn)水，系統(tǒng)水力停留時(shí)間約為24h，但隨進(jìn)水情況變化而略有所差異。采用COD和PV評(píng)估UASB系統(tǒng)的性能。 2．2 分析方法 每月均對(duì)進(jìn)水和出水采樣，兩天后出分析報(bào)告。采樣方式為采集均樣，24h為一個(gè)采樣周期，每小時(shí)采樣一次。測(cè)試所有水質(zhì)指標(biāo)以分析該日系統(tǒng)進(jìn)出水的水質(zhì)情況。(表2.1)是具體檢測(cè)程序，本文所采用的數(shù)據(jù)均為月平均值。 pH、COD、高錳酸鹽指數(shù)、總固體TS、總懸浮物TSS、可沉降固體、總?cè)芙庑怨腆wSS等指標(biāo)的分析采用標(biāo)準(zhǔn)方法。磷酸根和總氮采用德國(guó)Merck公司的Nova 60分光光度計(jì)測(cè)試，其檢測(cè)方法遵照使用說(shuō)明。 表2.1 檢測(cè)程序 監(jiān)控項(xiàng)目 樣品類型 分析 頻率 啤酒廢水（原廢水，集水池） 24h均樣 COD,PV,總硝基氮，磷酸鹽，pH，總固體，沉淀物。 每周三次 UASB進(jìn)水（平衡器出水） 瞬時(shí)樣/24h均樣 COD,PV,總固體，沉淀物，氮，磷酸鹽 每周三次 UASB出水 瞬時(shí)樣/24h均樣 COD,PV,pH ,總固體，沉淀物，氮，磷酸鹽 每周三次 3 結(jié)果與討論 3．1 無(wú)過(guò)濾啤酒廢水組成 未經(jīng)處理的無(wú)過(guò)濾啤酒廢水(原水)主要成分見(jiàn)(表2)。由于原水氮、磷含量較低，不足以提供厭氧菌生存所需的營(yíng)養(yǎng)，因而按COD：N：P：100：5：1的比例向原水添加尿素和磷酸鉀。據(jù)Ochieng等人報(bào)道：氮、磷含量豐富的啤酒廢水比一般啤酒廢水的COD去除率高。因原水呈酸性，故添加純堿調(diào)節(jié)其pH為中性。當(dāng)?shù)卣试S的廢水排放濃度見(jiàn)(表2) 由(表3.1)可以看出，未經(jīng)處理的無(wú)過(guò)濾啤酒廢水的水質(zhì)指標(biāo)不能達(dá)標(biāo)，其有機(jī)物和懸浮物濃度較高，而營(yíng)養(yǎng)物含量較低，適于用厭氧法處理。此類廢水類似于一般啤酒廢水，都是有機(jī)污染物含量較高，而營(yíng)養(yǎng)物含量較低。啤酒間歇生產(chǎn)特性造成了廢水水質(zhì)波動(dòng)較大，因而COD濃度變化較大，很難有一個(gè)叵定的有機(jī)負(fù)荷，這就需要采用適宜的污水處理系統(tǒng)。 本套UASB反應(yīng)器采用活性污泥接種，取代了常用的絮狀污泥或消化污泥，這主要是因?yàn)槠鋬?nèi)含有大量的甲烷菌，很容易繁殖。更為重要的是其生物活性強(qiáng)于消化污泥。 表3.1 處理前無(wú)過(guò)濾啤酒廢水水質(zhì) 參數(shù) 數(shù)值范圍 平均濃度±標(biāo)準(zhǔn)偏差（30個(gè)樣品） 哈拉雷市 允許排放濃度 pH 3.30－6.30 4.5±0.6 6.8－9.0 COD(mg/l) 8240≥20000 12535±4278 3000 總懸浮物（mg/l） 2901－3000 2841±175 600 總固體（mg/l） 5100－8750 7201±1606 總?cè)芙庑怨腆w（mg/l） 2020-5940 4520±1927 <2000 沉淀物（mg/l） 90-400 274±268 10 總氮（mg/l） 0.0196－0.0336 0.023±0.007 400 總磷酸鹽（mg/l） 16－124 59±52 10 高錳酸鹽指數(shù)（mg/l） 287－900 627±232 30 溫度（℃） 25－35 28±3 80 3．2 UASB反應(yīng)器的性能 在這兩年內(nèi)，無(wú)過(guò)濾啤酒廢水的UASB系統(tǒng)的性能見(jiàn)(圖1)。該污泥處理系統(tǒng)的最終出水pH為6．5～7．3。前三個(gè)月，UASB反應(yīng)器出水的COD仍然較高，這可能是由于進(jìn)水含有大量腐敗啤酒是原因之一。第四個(gè)月起，由于在集水池去除了大部分的懸浮物，UASB反應(yīng)器的性能明顯改善。第5月、第6月和第11月，腐敗啤酒造成反應(yīng)器出水COD濃度偏高；此外，泵出現(xiàn)機(jī)械故障也嚴(yán)重影響了整套污水處理系統(tǒng)。從第l2月開(kāi)始，COD去除率明顯提高，這主要是第11月增加了一套孔徑為0．5mm的細(xì)篩，減少了進(jìn)入?yún)捬醴磻?yīng)器的總固體量。第一道篩濾孔徑為1．0mm。在這兩年內(nèi)，該套UASB系統(tǒng)COD平均去除率為57％。Aysten-nann-Haun和Seyfried利用UASB反應(yīng)器處理過(guò)濾啤酒廢水的中試研究表明，其COD去除率可達(dá)80％。室溫下UASB反應(yīng)器的一項(xiàng)小試實(shí)驗(yàn)表明，其COD去除率高達(dá)89％，也就是說(shuō)，UASB反應(yīng)器的性能一般都能改善。 ●進(jìn)水COD 口出水COD ▲COD允許排放濃度(3g／L) , × COD去除率％ 有機(jī)負(fù)荷可用PV(高錳酸鹽指數(shù))表示見(jiàn)(圖2)。當(dāng)?shù)卣捎酶咤i酸鹽方法測(cè)試有機(jī)負(fù)荷，但采用重鉻酸鹽回流滴定的方法優(yōu)于高錳酸鹽方法，因此可用這兩種方法測(cè)試COD。研究期間，PV去除率為30～70％ ，平均為62％。從第14個(gè)月開(kāi)始，反應(yīng)器出水的PV基本降至允許排放濃度80mg／L。 第17個(gè)月起，反應(yīng)器處理效率有了明顯改善，其COD和PV各見(jiàn)(圖1)和(圖2)。反應(yīng)器進(jìn)水減少是其原因之一。此外，反應(yīng)器內(nèi)接種污泥馴化、逐步適應(yīng)來(lái)水水質(zhì)也可能是一個(gè)原因。(圖3)說(shuō)明了UASB反應(yīng)器總氮濃度的變化情況。一般來(lái)說(shuō)，無(wú)過(guò)濾啤酒廢水的氮含量較低，必須補(bǔ)充氮源來(lái)滿足厭氧菌的生長(zhǎng)需要。出水的總氮并不超標(biāo)(400mg／L)，但由于總氮會(huì)造成下游水體的富營(yíng)養(yǎng)化，并對(duì)甲烷菌具有一定毒性，因此必須監(jiān)控該項(xiàng)指標(biāo)。 UASB反應(yīng)器出水中總磷含量較高，高于當(dāng)?shù)卣脑试S排放濃度(見(jiàn)圖4)，這主要是由于在均衡池內(nèi)添加了三價(jià)磷酸鹽補(bǔ)充營(yíng)養(yǎng)。據(jù)文獻(xiàn)報(bào)道，由于UASB系統(tǒng)不能產(chǎn)生大量的污泥，因而對(duì)氮和磷的去除率較低。氮是厭氧菌生長(zhǎng)必須的營(yíng)養(yǎng)元素，在生物反應(yīng)器內(nèi)如果沒(méi)有積累有機(jī)物，進(jìn)水和出水的總氮應(yīng)該持平。氮和磷是水體的營(yíng)養(yǎng)元素，其富營(yíng)養(yǎng)化將引起藻類植物的過(guò)度繁殖。在后12個(gè)月，總磷相對(duì)較低。 總固體和可沉降固體的減少情況分別見(jiàn)(圖5)和(圖6)。UASB反應(yīng)器的總固體平均去除率為50％。在起初的10個(gè)月內(nèi)，總固體去除率低于40％ ，而從第11個(gè)月開(kāi)始，其去除率有了明顯的改善，提升到60％ ～8o％。這主要是由于在第11月安裝了一套孔徑為0．5mm的細(xì)篩。可沉降固體去除率為87％ ～9r7％ ，平均為90％?？沙两倒腆w是啤酒廢水的一個(gè)難題，需要在處理過(guò)程中監(jiān)控。 由于COD和總固體的平均去除率分別為57％和50％ ，因而必須改善UASB反應(yīng)器的性能。堿的不斷添加，不僅增加了處理成本，而且也讓生物系統(tǒng)極易失衡或者崩潰。這就需要尋找一個(gè)低廉的替代品來(lái)改善系統(tǒng)的緩沖能力。這套500m3處理系統(tǒng)產(chǎn)生的沼氣并沒(méi)有收集和檢測(cè)，而是未經(jīng)燃燒直接排放到大氣中。為更好地發(fā)展啤酒廢水處理工藝，沼氣的回收利用有著廣闊的發(fā)展空間。 4 結(jié)論 本研究中，UASB反應(yīng)器可將啤酒廢水的有機(jī)負(fù)荷降低到允許排放濃度以下。對(duì)啤酒廠而言，更大收益在于厭氧過(guò)程產(chǎn)生的甲烷氣，它既可作為蒸汽鍋爐的燃料，也可通過(guò)發(fā)電機(jī)轉(zhuǎn)化為電能。由此可以斷定，啤酒廠內(nèi)設(shè)置一套厭氧污水處理系統(tǒng)有其經(jīng)濟(jì)上的吸引力，同時(shí)，在這個(gè)能源缺乏、價(jià)格高昂的年代，這必將成為符合環(huán)保高要求的最佳選擇。 A study of industrial anaerobic treatment of opaque beer brewery wastewater in a tropical climate using a full-scale UASB reactor seeded with activated sludge W. Parawiraa, I. Kuditab, M. G. Nyandorohb and R. Zvauyaa a Department of Biochemistry, University of Zimbabwe, P.O. Box MP 167, Mount Pleasant, Harare, Zimbabwe b Chibuku Breweries, P.O. Box 3304, Southerton, Harare, Zimbabwe Received 1 August 2003;? accepted 17 January 2004.? Available online 11 June 2004. Abstract A full-scale upflow anaerobic sludge blanket (UASB) reactor treating traditional opaque beer brewery wastewater recently installed at an opaque beer factory was studied for 2 years. The total volume of the reactor was 500?m3 and the hydraulic retention time was approximately 24?h. The aim of the study was to evaluate the performance of the UASB reactor during anaerobic digestion of opaque beer brewery wastewater in terms of treatment efficiency. The untreated opaque beer wastewater has high solids content and high organic matter, which need pretreatment before it is discharged into municipal sewage treatment works. The UASB reactor enables the brewery to meet the requirements of the wastewater discharged into municipal sewerage system of Harare. The average percentage reduction in Chemical Oxygen Demand (COD) was 57%. The total and settleable solids were also reduced by 50 and 90%, respectively. The effluent from the UASB reactor contained higher orthophosphates and nitrogen levels than the influent leading to the accumulation of these nutrients in the system. These results indicated that the UASB plant was effective for treating opaque beer brewery wastewater at ambient temperature to meet the quality of effluent that can be discharged into public water works. Author Keywords: Anaerobic digestion; UASB; Opaque beer brewery wastewater; Chemical Oxygen Demand 1. Introduction The opaque beer brewery industry uses large volumes of water and discharges large volumes of effluent throughout the year, which are highly polluting. In Zimbabwe, there are 20 opaque beer breweries that produce over 420 million litres of opaque beer each year. The opaque beer brewing involves the blending of sorghum malt, and maize grits, followed by its subsequent fermentation with yeast. Essentially the process involves lactic acid fermentation as well as alcoholic fermentation. The beer is marketed and consumed whilst still actively fermenting. The brewing process employs a number of batch-type operations in processing raw materials to the final beer product. In the process large quantities of water are used for the production of beer itself, as well as for general washing of floors, and cleaning the brewhouse, cellars, packaging and cleaning in place, after each batch is completed. Due to the opaque beer brewery’s effluent characteristic high organic content and acidic nature, it has the potential to cause considerable environmental problems [1]. Such industrial effluents may result in reduction of the efficiency of the municipal treatment works [2]. The brewery effluents may affect water quality in many ways, including organic matter increase, and resultant increase in Biological Oxygen Demand (BOD5) and COD. The high organic loads in the wastewater arises from dissolved carbohydrates, the alcohol from beer wastes, and a high content of suspended solids, e.g. spent maize, malt, and yeast. In order to control pollution and protect the environment, brewery effluent containing high concentrations of organic matter cannot be discharged to sewers and watercourses. The municipal authority in Harare is placing severe restrictions on the quality of effluent which industry can discharge into their municipal system, which makes on-site pretreatment necessary for some types of effluent. The brewery effluent is composed of wastewaters from cleaning tanks, fermentation tanks, floors etc. [3]. A highly polluted effluent will reduce the capacity of the municipal wastewater treatment plant considerably and even overload such a plant. The implementation of low-cost, efficient, simple mitigation measures is required to enable the traditional opaque beer brewery industry to contribute to water conservation. For the breweries, there are aerobic and anaerobic biological treatment options. Zvauya et al. [1] reported the possibility of using thermophilic aerobic treatment of traditional opaque beer brewery wastewater. However, brewery effluent is categorised as medium-to-high-strength organic wastewater and requires an intensive amount of energy for aeration. Another mitigating factor is the large amount of waste sludge generated from these aerobic treatment processes, which also needs to be handled and disposed of and this increases the cost of operation of the treatment system. Austermann-Haun and Seyfried [4] reported that UASB plant at a brewery proved to be environmentally safer and more efficient than a high rate aerobic pretreatment plant. On the other hand, anaerobic digestion is a simple and reliable option with several advantages. The advantages of the process include the fact that less energy is required because no aeration is needed, the organic matter in the influent is partly converted to methane, which can be used for energy production, and less excess biomass and sludge are formed and therefore less disposal cost [5 and 6]. During anaerobic digestion organic pollutants are degraded by a consortia of microbial populations through multiple degradation steps such as hydrolysis/fermentation, acetogenesis and methanogenesis [7]. These anaerobic microbes, including fermentative bacteria, acetogenic bacteria and methanogens usually form a syntrophic relation [8]. Anaerobic digestion enables industry to comply with the stricter pollution control regulations, and also to satisfy the search for greater efficiency, better economy and the use of natural energy sources [9]. In recent years, there has been an increasing interest in the application of anaerobic digestion to brewery wastewater since the nature and strengths of the brewery wastewater often provides ideal conditions for the digester operations. However, there are problems associated with the start-up and operation of anaerobic treatment process due to the complexity of the process that is carried out by a consortium of unidentified and interdependent microorganisms, which makes the process unstable and difficult to monitor. Given the particularly complex and fluctuating nature of the brewery wastewater, it is clear that anaerobic digestion could be a sensitive to the changes in wastewater composition. Also the anaerobic treatment of many industrial effluents with low pH and high organic load has always been problematic as compared to other wastes of different origin, e.g. municipal wastes [10]. UASB reactors need not be unreliable if properly operated, monitored and controlled. The UASB wastewater (pre-) treatment systems represent proven sustainable technology for a wide range of very different industrial effluents [11, 12, 13 and 14]. The onus, therefore, rests both on the designer to provide reliable control arrangements and on the operator to devise overall monitoring and control strategies to minimise an overload risk. Despite the fact that the opaque beer brewing industry is big business in most African countries, there are very few breweries that are attempting to treat their waste. Brewery effluent treatment work has been largely on clear beer wastewater [5]. There are no published scientific reports of anaerobic digestion of opaque beer brewery wastewater using the anaerobic digestion technology to the best of our knowledge. The aim of this study was to evaluate the anaerobic digestion of opaque beer brewery wastewater from the largest opaque beer brewery in Harare, Zimbabwe using a recently installed UASB reactor. 2. Materials and methods 2.1. The reactor system used The industrial full-scale UASB reactor or clarigester at an opaque beer brewery in Harare was used in the study. The UASB reactor was constructed of concrete. The volume of the UASB reactor was 500?m3 based on the average organic loading rate of 6?kg COD/m3 per day. The effluent treatment plant consisted of a receiving tank, screens (0.5?mm mesh), balancing tank and the UASB reactor. The screens were used to remove heavy suspended solids. The balancing or buffering tank was used to balance the variations in organic loads, pH and flow resulting from batch operation of the brewing process as well as the dilution of toxic and inhibiting compounds from the processing plant. The nitrogen and phosphate nutrients supplements were added into the balancing tank in the form of urea and triple super phosphate. The nutrients were added to obtain a COD:N:P ratio of 100:5:1. The wastewater was acidic (pH 3.3–6.3) and thus soda ash was also added to adjust the influent pH to neutral. The wastewater emanating from the balancing tank was then fed into the bottom of the UASB reactor and the effluent discharged from the top together with the gas. The digester was originally seeded using a mixture of active municipal sludge, which was maintained at a temperature of approximately 37±2?°C for 3 months with intermittent feeding with brewery wastewater to acclimatise the bacteria to the feed substrate. The retention time was approximately 24?h although it varied with influent flow. The performance of the UASB system was monitored by measurement of the COD, and permanganate value (PV) in the influent and the effluent over a period of 2 years. 2.2. Analytical methods Chemical analyses were conducted on both the influent and effluent composite samples collected after two days throughout every month after commissioning of the plant. Samples were collected every hour over a 24-h period and the measurement of the parameters was done to determine the overall parameter profile of the total brewery effluent for that day. The monitoring and reporting programme followed in this study was as shown below (Table 1). The mean value and the range for the month were reported in the monthly report of operation. The results presented here are monthly averages. Table 1. Monitoring programme employed in this study The following parameters were monitored and analysed according to standard methods: pH, COD, permanganate value, total solids (TS), total suspended solids, settleable solids, total dissolved solids [15]. The amounts of orthophosphates and total nitrogen were measured with the test kits according to manufacturer’s instruction (Merck, Germany) using a Spectroquant Nova 60 photometer (Merck, Germany). 3. Results and discussion 3.1. Opaque beer brewery effluent composition The average composition of opaque beer brewery wastewater from the opaque beer brewery before treatment is given in Table 2. The wastewater required nutritive and pH conditioning before it entered the reactor. As the raw wastewater was unable to provide sufficient nutrients for anaerobic microorganisms, urea and potassium phosphate were added to give a COD:N:P of 100:5:1. Ochieng et al. [16] reported a higher COD reduction with nitrates and phosphates enriched brewery wastewater compared with wastewater without nutrient enrichment. The effluent was acidic, thus, soda ash was also added to adjust the influent pH to neutral pH. The permissible limits of components in effluent discharged into public water are also shown in Table 2. As can be seen the levels of water quality parameters do not meet the effluent standards of the local authority. The results indicate that the untreated opaque beer brewery wastewater has high organic matter and suspended solids and low concentrations of nutrients. They is the type of wastewater for which anaerobic digestion would be an acceptable treatment method [17]. The characteristic high concentrations of organic pollutants and low nutrient content characterised by large variations in these parameters is consistent with wastewater from clear beer breweries [3 and 11]. The fluctuations in the wastewater characteristics are due to changes in what is happening in the plant during each period and discontinuous discharges of the brewery’s departments. Owing to the large fluctuations in the strength of the brewery wastewater, the influent COD concentration showed large variations, making it difficult to use a constant organic loading rate. There is need for on-site treatment of the wastewater to protect the environment and reduce costs as heavy penalties are imposed for discharging substandard effluent into the urban treatment works. Table 2. Opaque beer brewery wastewater characteristics before treatment Activated sludge was chosen to seed the UASB reactor instead of pre-granulated bacterial flocs or digested sewage sludge because a considerable amount of methanogenic bacteria is found in activated sludge and it is easy to obtain large amounts. More importantly activated sludge contains little sand or soil and is composed mostly of biomass unlike digested sewage sludge [11]. 3.2. Performance of the UASB clarigester The performance of the UASB plant at the opaque beer brewery was studied over a period of 2 years (Fig. 1). The final effluent from the wastewater treatment plant had a pH between 6.5 and 7.3. For first 3 months of the study, the effluent from the digester had high levels of COD remaining after treatment. This may have been probably due to the presence of suspended solids in the influent. There was a lot of bad beer destruction in these months as well. The total solids in the influent to the anaerobic digester were reduced as from the fourth month by removing solids from the bottom of the receiving tank, and the performance of the reactor improved. In the 5th, 6th and 11th month the effluent from the reactor had high COD because of beer destruction. The brewery was discharging spoilt beer into the effluent plant during these months. Furthermore the whole wastewater treatment plant also suffered heavily from pump mechanical breakdowns in these months. During pump breakdowns the influent was discharged directly into the municipal sewers. The average COD removal efficiency was 57% for the period of this study. The COD removal efficiency improved from the 12th month to the end of the study period. This was due to installation of a screen with a smaller mesh size (0.5?mm) in the 11th month, which reduced the quantity of total solids entering the digester. The first screen had a mesh size of 1.0?mm. The COD removal efficiency achieved in this study is comparable to an average of 60% obtained in a comparative laboratory-scale study of the effects of dairy and clear beer brewery effluents on the treatability of domestic sewage by Kilani [2]. However, Stadlbauer et al. [18] reported COD removal efficiencies of 85 to 90% from a study of anaerobic purification of lager beer brewery wastewater in laboratory scale biofilm reactors with and without a methanation cascade. Austermann-Haun and Seyfried [4] also reported 80% COD removal efficiency from a pilot-scale UASB reactor treating clear bee