宋歡,張光明,王洪臣,楊安琪,楊光(中國(guó)人民大學(xué) 環(huán)境學(xué)院,北京 100872)
污泥與其它基質(zhì)共消化研究進(jìn)展
宋歡,張光明,王洪臣,楊安琪,楊光
(中國(guó)人民大學(xué) 環(huán)境學(xué)院,北京100872)
厭氧消化是污泥處理的有效手段,但由于污泥碳氮比較低,易產(chǎn)生氨抑制,污泥單獨(dú)厭氧消化存在產(chǎn)氣量低,系統(tǒng)不穩(wěn)定等問(wèn)題。污泥與其它基質(zhì)厭氧共消化可以提高甲烷產(chǎn)率與單位處理效率,有效解決系統(tǒng)不穩(wěn)定的問(wèn)題。針對(duì)污泥厭氧共消化進(jìn)行了系統(tǒng)的研究,總結(jié)了基質(zhì)的主要來(lái)源,就不同基質(zhì)共消化時(shí)體系運(yùn)行參數(shù)、系統(tǒng)抑制與強(qiáng)化因子進(jìn)行了分析,發(fā)現(xiàn)作為共消化基質(zhì)的餐廚垃圾可以得到廣泛應(yīng)用,油脂類(lèi)或藻類(lèi)物質(zhì)的應(yīng)用逐漸上升,污泥與基質(zhì)投配比、溫度、反應(yīng)器類(lèi)型、預(yù)處理等均能影響共消化的效果。對(duì)污泥與其它基質(zhì)共消化的發(fā)展方向提出了建議和展望。
污泥;基質(zhì);共消化;碳氮比
近年來(lái),隨著我國(guó)污水處理廠(chǎng)不斷建成、投入使用,污泥產(chǎn)量大幅提升,到2014年,全國(guó)城鎮(zhèn)污水處理廠(chǎng)干污泥(80%含水率)產(chǎn)生量已達(dá)667.5萬(wàn)t[1]。污泥厭氧消化可有效實(shí)現(xiàn)污泥減量化、無(wú)害化、資源化,已被廣泛運(yùn)用到實(shí)際中。但污泥碳氮比較低,在中溫條件下產(chǎn)甲烷率最高只達(dá)150 mL/g[VSadded][2],且消化過(guò)程中的氨抑制等問(wèn)題限制了污泥厭氧消化技術(shù)的進(jìn)一步推廣[3]。
共消化指2種或多種基質(zhì)同時(shí)進(jìn)行厭氧消化,能有效提升產(chǎn)甲烷效率。在污泥厭氧共消化過(guò)程中,污泥與其它基質(zhì)形成良性互補(bǔ),在不同基質(zhì)的協(xié)同作用和菌群多樣性、基質(zhì)中有害成分(如重金屬、致病菌等)的稀釋作用下,消化過(guò)程變得更加穩(wěn)定,產(chǎn)氣量上升。污泥與其它基質(zhì)共消化使生物質(zhì)能輸出能力加強(qiáng),提升污泥資源化能力。對(duì)于污水處理廠(chǎng)來(lái)說(shuō),可充分利用現(xiàn)有設(shè)備進(jìn)行共消化,在提高厭氧消化池處理能力的同時(shí),還可接收其它廢物并收取處理費(fèi)用,提高經(jīng)濟(jì)收益。污泥與其它基質(zhì)共消化已成為污泥處理的有效方式。
基質(zhì)是指經(jīng)過(guò)厭氧菌消化可以產(chǎn)生甲烷的任何物質(zhì),其來(lái)源廣泛。從國(guó)內(nèi)外近十多年的研究文獻(xiàn)分析,基質(zhì)來(lái)源主要分為農(nóng)業(yè)來(lái)源、工業(yè)來(lái)源與城市社區(qū)來(lái)源3類(lèi),其中城市社區(qū)來(lái)源研究最多,占68.4%,工業(yè)來(lái)源占16.2%,農(nóng)業(yè)來(lái)源占12.8%。
共消化體系的碳氮比是決定消化過(guò)程穩(wěn)定性與產(chǎn)氣量的重要因素。共消化基質(zhì)相比污泥具有較高的碳氮比。因此,污泥與其它基質(zhì)共消化可有效緩解污泥厭氧消化中碳源不足的問(wèn)題。典型污泥厭氧共消化基質(zhì)的碳氮比如圖1所示。
厭氧共消化基質(zhì)的農(nóng)業(yè)來(lái)源包括:畜牧業(yè)副產(chǎn)品、農(nóng)作物剩余廢物與能源植物(包括藻類(lèi))等,其中藻類(lèi)由于具有比陸生植物更強(qiáng)的產(chǎn)甲烷能力與效率而受到廣泛關(guān)注。
2.1畜牧業(yè)副產(chǎn)品
養(yǎng)殖場(chǎng)排放垃圾包括糞便、過(guò)期飼料等。牛糞與豬糞含有大量礦物質(zhì)元素和豐富的營(yíng)養(yǎng)物質(zhì),碳氮比為9.7~18.7,與污泥共消化可以提升產(chǎn)氣量與緩沖能力[4]。牛糞與豬糞還含有瘤胃微生物,可協(xié)助厭氧消化更快進(jìn)行,縮短HRT,提高產(chǎn)氣效率[5]。
多數(shù)研究發(fā)現(xiàn)動(dòng)物糞便與污泥共消化最佳HRT多在20 d左右,隨著HRT的縮短和有機(jī)負(fù)荷(OLR)的提升,甲烷產(chǎn)量減少。這是因?yàn)樵诠蚕到y(tǒng)中,有機(jī)成分及有機(jī)物降解程度對(duì)消化過(guò)程有著重要的影響。合理的投配比是厭氧共消化成功的必要條件,劉一威[6]研究發(fā)現(xiàn)污泥和動(dòng)物糞便垃圾的TS投加比例應(yīng)控制在40%以下。類(lèi)似的結(jié)論也由Pitk等[7]得出,在體系中添加10%以上的畜牧副產(chǎn)品導(dǎo)致體系發(fā)泡現(xiàn)象嚴(yán)重,長(zhǎng)鏈脂肪酸積累過(guò)多,游離氨產(chǎn)生過(guò)多。
2.2農(nóng)業(yè)纖維素類(lèi)廢物
農(nóng)業(yè)纖維素類(lèi)廢物包括谷物收獲后的剩余廢物與能源植物等。應(yīng)用于污泥厭氧共消化的基質(zhì)主要有秸稈、橄欖果渣、能源植物等。秸稈主要成分為纖維素,其碳氮比多在35以上,是補(bǔ)充污泥低碳氮比的良好基質(zhì)。Kim等[8]發(fā)現(xiàn)污泥與秸稈厭氧共消化產(chǎn)氫的最佳碳氮比為25∶1。在袁海榮等[9]的研究中也有類(lèi)似的發(fā)現(xiàn),當(dāng)碳氮比為25∶1時(shí),秸稈與污泥混合基質(zhì)產(chǎn)氣量最大。
不同的反應(yīng)器對(duì)厭氧消化系統(tǒng)有較大影響。利用兩相反應(yīng)器,將污泥與秸稈共消化的產(chǎn)氫階段與產(chǎn)甲烷階段分離,可提高37.9%的VS去除率和59.6%的總沼氣產(chǎn)量[10],相似的結(jié)論也可在污泥與木薯臺(tái)厭氧共消化的研究中得到[11]。這是因?yàn)閮上喾磻?yīng)器將不同階段分離,降低了菌群競(jìng)爭(zhēng)。
2.3藻類(lèi)
藻類(lèi)具有較低的木質(zhì)素、更易水解的糖分和蛋白質(zhì),在厭氧消化中有利于水解的進(jìn)行,它同時(shí)具有較高的生長(zhǎng)速度與適應(yīng)性,可直接在污水處理廠(chǎng)投加并培養(yǎng)。與污泥進(jìn)行厭氧共消化的藻類(lèi)通常包括微藻、柵藻、小球藻、鈍頂螺旋藻等。
藻類(lèi)與污泥厭氧共消化可有效提高VS去除率和水解速率。Olsson等[12]研究發(fā)現(xiàn),在中溫條件下,微藻與污泥共消化產(chǎn)甲烷率可達(dá)到(408±16)cm3/g[VS],高溫情況下未發(fā)現(xiàn)產(chǎn)氣量提升,可能是因?yàn)橄嚓P(guān)菌群在中溫條件下具有較高活性。Wang等[13]研究發(fā)現(xiàn),柵藻和小球藻與污泥厭氧消化時(shí),相比于污泥單獨(dú)消化甲烷產(chǎn)率并未提升。有些藻類(lèi)與污泥共消化有利于提升污泥脫水性能,例如柵藻、鈍頂螺旋藻等,而小球藻對(duì)污泥脫水性能有輕微不良影響[14]。以上研究表明不同藻類(lèi)與污泥厭氧共消化的效果存在一定差異,應(yīng)在理論與試驗(yàn)的基礎(chǔ)上選擇合適的藻種與污泥進(jìn)行共消化。
2.4污泥與農(nóng)業(yè)來(lái)源基質(zhì)厭氧共消化主要運(yùn)行參數(shù)及效果
圖1 典型污泥厭氧共消化基質(zhì)的碳氮比
表1 污泥與農(nóng)業(yè)來(lái)源基質(zhì)厭氧共消化主要運(yùn)行參數(shù)及效果Tab.1 Main operating parameters and effect of sludge and agricultural substrates anaerobic co-digestion
污泥與農(nóng)業(yè)來(lái)源基質(zhì)厭氧共消化主要運(yùn)行參數(shù)及效果如表1所示。從表1可見(jiàn),根據(jù)不同基質(zhì)特性和污泥性質(zhì),基質(zhì)和污泥有不同的投配比,多采用中溫與批次試驗(yàn)方法,甲烷產(chǎn)率最高可提升5.7倍,VS降解率多在40%~60%之間。農(nóng)業(yè)來(lái)源基質(zhì)消化體系較為穩(wěn)定,較少產(chǎn)生系統(tǒng)抑制。
工業(yè)基質(zhì)包括生物柴油產(chǎn)業(yè)、食品加工業(yè)及其它工業(yè)有機(jī)廢物。生物柴油產(chǎn)業(yè)主要副產(chǎn)品為粗甘油;食品加工業(yè)包括肉類(lèi)加工業(yè)、奶制品加工業(yè)、制酒工業(yè)、淀粉加工業(yè)、制糖工業(yè)等。
3.1粗甘油
粗甘油含碳量較高[17],可作為碳源被消化菌吸收利用,因此可調(diào)節(jié)共消化體系的碳氮比,并稀釋有毒物質(zhì)。中溫是粗甘油與污泥厭氧共消化的適宜溫度,Silvestre等[17]發(fā)現(xiàn)在高溫條件下系統(tǒng)pH值下降嚴(yán)重。
粗甘油與污泥共消化應(yīng)嚴(yán)格控制粗甘油投加量。Fountoulakis等[18]發(fā)現(xiàn)投加甘油體積分?jǐn)?shù)大于3%時(shí)會(huì)導(dǎo)致系統(tǒng)崩潰。Razaviarani等[19]也發(fā)現(xiàn)隨著甘油投加量的增加,VFA含量上升,而pH值、堿度和產(chǎn)氣量下降。Nartker等[20]發(fā)現(xiàn)通過(guò)控制投加速度與方式,細(xì)菌種群可及時(shí)調(diào)整適應(yīng),當(dāng)OLR為70%時(shí)仍可保持系統(tǒng)穩(wěn)定。這表明在實(shí)際運(yùn)行中采用合適的投加方式與速度可提高甘油的投配比,提高處理率。污泥與粗甘油厭氧共消化會(huì)降低污泥的脫水性能[17]。
3.2食品加工業(yè)廢物
食品加工業(yè)廢物的碳氮比在17.2~39.1之間。脂肪酸的積累對(duì)產(chǎn)甲烷菌的毒害作用、系統(tǒng)pH值下降、過(guò)高的OLR與過(guò)低的HRT是共消化系統(tǒng)的主要抑制因素。
Neves等[21]在研究污泥和咖啡加工廢物厭氧共消化過(guò)程中,發(fā)現(xiàn)水解速率常數(shù)與甲烷產(chǎn)率呈逆相關(guān),原因可能是水解中間產(chǎn)物對(duì)產(chǎn)甲烷菌具有毒害作用。Li等[22]發(fā)現(xiàn)可向咖啡加工廢物與污泥共消化系統(tǒng)中添加硫酸鹽以調(diào)節(jié)丙酸降解細(xì)菌的菌群活性,可增加甲烷產(chǎn)量。Fernández等[23]在研究污泥與乳清共消化時(shí)發(fā)現(xiàn),高溫下產(chǎn)氣速率較高,但甲烷總產(chǎn)率較中溫降低。Koupaie等[24]對(duì)污泥與果汁生產(chǎn)廢物厭氧共消化進(jìn)行成本效益分析,發(fā)現(xiàn)相比于2個(gè)單獨(dú)的消化器,采用共消化可節(jié)省總成本27.6%。
3.3污泥與工業(yè)來(lái)源基質(zhì)厭氧共消化主要運(yùn)行參數(shù)及效果
污泥與工業(yè)來(lái)源基質(zhì)厭氧共消化主要運(yùn)行參數(shù)及效果如表2所示。與其它基質(zhì)相比,工業(yè)基質(zhì)與污泥厭氧共消化更容易產(chǎn)生系統(tǒng)抑制,具體表現(xiàn)為OLR過(guò)高、揮發(fā)性脂肪酸積累、系統(tǒng)pH值下降等。粗甘油與污泥厭氧共消化應(yīng)嚴(yán)格控制投加量,多采用中溫CSTR反應(yīng)器,HRT為18~24 d,甲烷產(chǎn)率可提升83%~148%,VS降解率在50%以上。同時(shí),食品加工業(yè)廢物也多采用中溫消化,甲烷產(chǎn)率最高可提升 1.87倍[25],VS降解率在23.4%~91.0%之間。工業(yè)基質(zhì)來(lái)源廣泛,投配比應(yīng)根據(jù)不同基質(zhì)進(jìn)行調(diào)整。
與污泥進(jìn)行厭氧共消化的基質(zhì)中,城市社區(qū)來(lái)源最為廣泛。具體可分為有機(jī)城市垃圾、隔油池廢物與其它廢物。有機(jī)城市垃圾包括餐廚與果蔬垃圾、庭院垃圾與其它城市固體廢棄物等。隔油池廢物主要來(lái)自食品服務(wù)行業(yè)與水廠(chǎng)浮選設(shè)施,具有較高油脂含量,可生化性強(qiáng)。其它城市社區(qū)來(lái)源廢物包括垃圾瀝出液、水廠(chǎng)泡沫浮渣等。
表2 污泥與工業(yè)來(lái)源基質(zhì)厭氧共消化主要運(yùn)行參數(shù)及效果Tab.2 Main operating parameters and effect of sludge and industrial substrates anaerobic co-digestion
4.1有機(jī)城市垃圾
城市垃圾有機(jī)成分具有良好的生物可降解性,但污泥與城市垃圾有機(jī)成分厭氧共消化系統(tǒng)需要較復(fù)雜的調(diào)控機(jī)制,且往往需要對(duì)城市垃圾進(jìn)行預(yù)處理。有機(jī)城市垃圾與污泥共消化體系預(yù)處理方法主要包括熱處理[28]、超熱預(yù)處理[29]、微波處理[30]等。
餐廚垃圾是目前的研究熱點(diǎn),其產(chǎn)量大,具有較好的生物可降解性。餐廚垃圾與污泥厭氧共消化可最高為污水處理廠(chǎng)提供50%以上的能量,是污泥單獨(dú)厭氧消化的2倍[31],在實(shí)際運(yùn)行中具有重大意義。投配比是影響系統(tǒng)表現(xiàn)的重要因素,Jang等[32]發(fā)現(xiàn)有機(jī)物去除率隨餐廚垃圾瀝出液投加比例增加而線(xiàn)性升高,但在瀝出液?jiǎn)为?dú)厭氧消化時(shí)下降,這顯示出污泥與餐廚垃圾共消化具有明顯的協(xié)同作用。
4.2隔油池廢物
隔油池廢物可分為3層,包括上層的油脂類(lèi)物質(zhì)、中間層食品廢水、下層的食物殘?jiān)糠帧8粲统貜U物含高油脂,在與污泥共厭氧消化時(shí)油脂類(lèi)物質(zhì)投配比過(guò)高,易造成廢水系統(tǒng)管道堵塞與腐蝕。共消化系統(tǒng)中,過(guò)高的有機(jī)負(fù)荷不利于厭氧消化系統(tǒng)的穩(wěn)定進(jìn)行,會(huì)造成長(zhǎng)鏈脂肪酸或揮發(fā)性脂肪酸的積累,導(dǎo)致系統(tǒng)酸化。因此,嚴(yán)格控制有機(jī)負(fù)荷是十分必要的。
整理、統(tǒng)計(jì)相關(guān)文獻(xiàn)中停留時(shí)間在20 d左右的CSTR或半連續(xù)流反應(yīng)器,考察中溫條件下共消化隔油池廢物負(fù)荷與甲烷產(chǎn)率的關(guān)系,擬合后的結(jié)果如圖2所示。由圖2可以發(fā)現(xiàn),隔油池廢物負(fù)荷在1.5 g[VS]/(L·d)左右時(shí)甲烷產(chǎn)率較高。
圖2 污泥與隔油池廢物厭氧共消化中隔油池廢物有機(jī)負(fù)荷與甲烷產(chǎn)率的關(guān)系
很多研究者發(fā)現(xiàn)利用未脫水隔油池廢物與污泥進(jìn)行厭氧共消化[33],可減少系統(tǒng)抑制的發(fā)生,主要原因是隔油池廢物稀釋了污泥中的有害成分。緩慢加入隔油池廢物可有效提升脂質(zhì)的降解,有利于相應(yīng)菌群適應(yīng)長(zhǎng)鏈脂肪酸含量逐漸升高,從而減少長(zhǎng)鏈脂肪酸的積累,提高隔油池廢物閾值與相應(yīng)的產(chǎn)氣量。Martínez等[34]發(fā)現(xiàn)脂質(zhì)的吸附作用可能阻礙了基質(zhì)的降解,可通過(guò)向系統(tǒng)中添加脂肪酶,促進(jìn)脂質(zhì)降解[35]。利用兩相反應(yīng)器可提升產(chǎn)氣量,且可節(jié)省建設(shè)與運(yùn)行費(fèi)用。此外,高溫條件下隔油池廢物與污泥厭氧共消化可減少H2S的產(chǎn)生,有利于系統(tǒng)穩(wěn)定[36]。
4.3污泥與城市社區(qū)來(lái)源基質(zhì)厭氧共消化主要運(yùn)行參數(shù)及效果
污泥與城市社區(qū)來(lái)源基質(zhì)厭氧共消化主要運(yùn)行參數(shù)及效果如表3所示。有機(jī)城市垃圾與污泥厭氧共消化可提升甲烷產(chǎn)率27%~169%,VS降解率在34%~95%之間。投配比與消化器根據(jù)不同基質(zhì)有較大區(qū)別,多采用中溫條件,HRT為20 d左右。隔油池廢物與污泥共消化多采用中溫連續(xù)或半連續(xù)消化,HRT為15~25 d時(shí),VS降解率在60%左右。
表3 污泥與城市社區(qū)來(lái)源垃圾厭氧共消化主要運(yùn)行參數(shù)及效果Tab.3 Main operating parameters and effect of sludge and community garbage anaerobic co-digestion
由于協(xié)同效應(yīng)與稀釋作用,污泥與其它基質(zhì)厭氧共消化能有效緩解厭氧消化中的不良影響,穩(wěn)定消化系統(tǒng),提高甲烷產(chǎn)率。
污泥與基質(zhì)投配比應(yīng)根據(jù)其性質(zhì)嚴(yán)格控制,避免過(guò)載而導(dǎo)致系統(tǒng)抑制。污泥厭氧共消化多采用中溫消化,系統(tǒng)較高溫穩(wěn)定,且實(shí)際運(yùn)行中能耗較少。采用兩相反應(yīng)器(溫度兩相分離反應(yīng)器或產(chǎn)酸-產(chǎn)甲烷相分離反應(yīng)器)較單相反應(yīng)器有更好表現(xiàn)。
共基質(zhì)的預(yù)處理往往能提高共消化系統(tǒng)甲烷產(chǎn)量,但應(yīng)進(jìn)一步分析多產(chǎn)生的甲烷生物質(zhì)能是否可以彌補(bǔ)預(yù)處理所耗能量。其它強(qiáng)化手段例如投加微量元素或相關(guān)酶是未來(lái)污泥厭氧共消化的研究方向之一。
采用污水廠(chǎng)自身產(chǎn)生的油脂、藻類(lèi)物質(zhì)共消化,或與其它基質(zhì)共消化,形成污泥減量化、無(wú)害化、資源化的產(chǎn)業(yè)鏈條,在提高環(huán)保效益的同時(shí),實(shí)現(xiàn)經(jīng)濟(jì)收益應(yīng)是今后努力的方向。
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Research progress of co-digestion of sludge and other substrates
SONG Huan,ZHANG Guang-ming,WANG Hong-chen,Yang An-qi,YANG Guang
(School of Environment and Natural Resources,Renmin University of China,Beijing 100872,China)
Anerobic digestion is an effective method for sludge treatment.However,ammonia inhibition is a common problem due to the low C/N ratio of sludge.Many problems such as low biogas production and unstable operation are existed during the single anaerobic digestion of the sludge.Co-digestion of sludge and other substrates is an effective solution to increase the methane yield and the treatment efficiency and eliminate the system instability.The co-digestion of anaerobic sludge was studied systematically and the source of substrates was summarized;besides,the operating parameters,system inhibition,and strengthening factors during the co-digestion with different substrates were analyzed.It was found that,kitchen waste was the most common co-digestion substrates,while the application of fats,oil,grease and algae were increasing in recent years.Sludge and substrates mixing ratio,temperature,reactor type,pretreatment and some other factors could affect the performance of co-digestion.Finally,the development tendency of co-digestion of sludge and other substrates was proposed and prospected.
sludge;substrate;co-digestion;C/N ratio
X703.1
A
1009-2455(2016)04-0001-06
國(guó)家自然科學(xué)基金項(xiàng)目(51278489)
宋歡(1995-),女,天津人,本科,研究方向?yàn)槲勰鄿p量化與資源化,(電子信箱)songhuan199510@163.com;通訊作者:張光明(1973-),女,湖南永州人,教授,研究生,研究方向?yàn)樗c廢水處理,(電子信箱)zgm@ruc.edu.com。
2016-04-25(修回稿)