畜禽養(yǎng)殖惡臭物質(zhì)組成與測(cè)定及評(píng)估方法研究進(jìn)展

劉 波， 王文林， 劉 筱， 范 婤， 楊婉靜， 徐 喬， 關(guān) 雷， 曾杰亮， 李文靜， 何 斐①

(1.南通大學(xué)地理科學(xué)學(xué)院， 江蘇 南通 226007； 2.環(huán)境保護(hù)部南京環(huán)境科學(xué)研究所， 江蘇 南京 210042)

畜禽養(yǎng)殖惡臭物質(zhì)組成與測(cè)定及評(píng)估方法研究進(jìn)展

劉 波1， 王文林2， 劉 筱1， 范 婤2， 楊婉靜1， 徐 喬1， 關(guān) 雷1， 曾杰亮1， 李文靜2， 何 斐2①

(1.南通大學(xué)地理科學(xué)學(xué)院， 江蘇 南通 226007； 2.環(huán)境保護(hù)部南京環(huán)境科學(xué)研究所， 江蘇 南京 210042)

隨著我國畜禽養(yǎng)殖業(yè)的迅速發(fā)展，惡臭已成為引發(fā)周邊居民投訴和糾紛的主要環(huán)境問題，嚴(yán)重制約了畜禽養(yǎng)殖業(yè)的可持續(xù)發(fā)展。因此，識(shí)別畜禽養(yǎng)殖惡臭來源及物質(zhì)組成、總結(jié)惡臭測(cè)定技術(shù)和了解惡臭表征與評(píng)估方法，對(duì)于科學(xué)評(píng)估惡臭危害進(jìn)而針對(duì)性地提出控制措施具有重要意義。系統(tǒng)梳理了畜禽惡臭物質(zhì)的主要組成與特征，對(duì)比分析了畜禽惡臭主要測(cè)定技術(shù)的優(yōu)缺點(diǎn)，討論了主要的惡臭表征評(píng)估方法。畜禽惡臭中起關(guān)鍵作用的物質(zhì)主要是揮發(fā)性脂肪酸類、含硫化合物、芳香族化合物(主要是酚類和吲哚)以及氨和揮發(fā)性胺類4類物質(zhì)。畜禽惡臭的測(cè)定方法大致分為儀器分析法和嗅覺法2類，2類方法各有優(yōu)劣。在分析現(xiàn)有惡臭成分的基礎(chǔ)上，判別畜禽惡臭的關(guān)鍵物質(zhì)，實(shí)現(xiàn)畜禽惡臭的現(xiàn)場(chǎng)連續(xù)監(jiān)測(cè)是今后研究的熱點(diǎn)。針對(duì)惡臭成分的復(fù)雜性，構(gòu)建惡臭物質(zhì)濃度與惡臭強(qiáng)度間的合理轉(zhuǎn)化關(guān)系是進(jìn)行惡臭評(píng)估的一種可行方法。

畜禽養(yǎng)殖； 惡臭物質(zhì)； 測(cè)定方法； 評(píng)估方法

隨著經(jīng)濟(jì)發(fā)展和人民生活水平的不斷提高,畜產(chǎn)品的需求量逐漸增大,專業(yè)化、規(guī)模化的畜禽養(yǎng)殖業(yè)得到迅速發(fā)展。但是,在畜禽養(yǎng)殖業(yè)迅速發(fā)展的同時(shí),其帶來的環(huán)境問題也日益凸顯[1]。大量的畜禽廢棄物對(duì)水體、土壤、大氣等產(chǎn)生了嚴(yán)重污染[2-3],其中,畜禽養(yǎng)殖造成的惡臭問題越來越引起關(guān)注。畜禽養(yǎng)殖產(chǎn)生的惡臭不但氣味令人厭惡,而且伴隨著病原微生物、懸浮顆粒、寄生蟲卵、氨氣、硫化氫等有毒有害成分,造成嚴(yán)重的空氣污染,威脅人畜的身心健康[4]。養(yǎng)殖場(chǎng)散發(fā)的惡臭已成為引發(fā)周邊居民投訴和糾紛的主要環(huán)境問題,被稱為“畜產(chǎn)公害”,嚴(yán)重制約了畜禽養(yǎng)殖業(yè)的可持續(xù)發(fā)展[5-6]。20世紀(jì)60年代以來,歐美國家在對(duì)惡臭成分開展鑒定分析和科學(xué)評(píng)估的基礎(chǔ)上,出臺(tái)了一系列惡臭監(jiān)測(cè)與管理標(biāo)準(zhǔn)和法規(guī)[7]。畜禽惡臭釋放源多樣,物質(zhì)組成復(fù)雜,且隨著惡臭物質(zhì)分析測(cè)試技術(shù)的發(fā)展,新惡臭成分不斷被發(fā)現(xiàn)。由此,識(shí)別畜禽養(yǎng)殖惡臭來源及物質(zhì)組成、總結(jié)惡臭測(cè)定技術(shù)和了解惡臭表征與評(píng)估方法,對(duì)于判別畜禽惡臭關(guān)鍵物質(zhì)、科學(xué)評(píng)估惡臭危害,進(jìn)而針對(duì)性地提出控制措施具有重要意義。基于此,筆者就畜禽養(yǎng)殖惡臭來源與組成、測(cè)定技術(shù)及表征評(píng)估方法的國內(nèi)外研究現(xiàn)狀進(jìn)行歸納總結(jié),并對(duì)今后的研究方向進(jìn)行簡(jiǎn)要展望。

1 來源與種類組成

1.1 來源與形成

畜禽養(yǎng)殖場(chǎng)惡臭排放源主要有畜禽舍、糞污貯存裝置與處理場(chǎng)所(堆肥車間、污水池等)、飼料間和糞污施用區(qū)域等[8]。有調(diào)查顯示,關(guān)于惡臭的投訴大約50%涉及施糞過程,20%涉及糞污貯藏場(chǎng)所,30%涉及畜禽舍[9-10]。隨著注入式施肥技術(shù)的應(yīng)用,歐洲國家的惡臭投訴更多涉及糞污處理設(shè)施和畜禽舍[11]。但是,目前尚無關(guān)于各排放源對(duì)畜禽惡臭貢獻(xiàn)率的系統(tǒng)研究[12]。

從惡臭形成過程來看,惡臭物質(zhì)主要是畜禽廢棄物,包括糞尿,溢灑飼料及廢水,墊料，廢水等在厭氧條件下發(fā)酵產(chǎn)生的揮發(fā)性化合物和氣體,其中,絕大部分為揮發(fā)性有機(jī)物(volatile organic compounds, VOCs)[13-14]。而在好氧條件下,畜禽廢棄物一般不會(huì)產(chǎn)生惡臭物質(zhì)[15]。畜禽糞尿被認(rèn)為是惡臭物質(zhì)最主要的來源[16]。育成豬消化道內(nèi)容物中檢測(cè)到吲哚、糞臭素,表明糞便在結(jié)腸和直腸中已開始腐敗,故新鮮糞便也具有一定的臭味[17]。而排出后的糞便在土著微生物、外源微生物等腐敗性微生物作用下繼續(xù)厭氧分解,導(dǎo)致惡臭強(qiáng)度迅速升高;同時(shí)鮮尿中的尿素和酚類聚合體,會(huì)因糞便的混入而急劇分解,揮發(fā)出氨(NH3)和酚類物質(zhì),導(dǎo)致惡臭加劇[18]。研究已發(fā)現(xiàn)形成惡臭的基質(zhì)主要是隨糞尿一起排出的未降解蛋白質(zhì)和易發(fā)酵碳水化合物[19-20]。蛋白質(zhì)在腐敗性微生物作用下分解產(chǎn)生各種氨基酸后通過氨基酸脫羧和脫氨作用形成惡臭物質(zhì)散發(fā)到環(huán)境中[21]。例如,氨基酸在高pH值條件下可產(chǎn)生NH3和揮發(fā)性脂肪酸(volatile fat acids, VFAs)[22];色氨酸和酪氨酸分解產(chǎn)生酚類和吲哚類物質(zhì)[23];胱氨酸生成了硫化氫;蛋氨酸生成了甲硫醇、二甲硫、乙硫醇等含硫化合物類惡臭物質(zhì)[24]。畜禽排泄物中的碳水化合物在厭氧發(fā)酵過程中可以形成乙酸、丙酸和丁酸[25]。

1.2 組成與特性

自1963年在豬糞中鑒定出硬脂酸(stearic acid)以來,人們對(duì)于畜禽養(yǎng)殖惡臭物質(zhì)的鑒定已有50多年的歷史[26]。隨著分析測(cè)試技術(shù)的發(fā)展,被鑒定出的惡臭物質(zhì)種類不斷增多,一次性鑒定出的惡臭物質(zhì)種類從20多到400多種不等,去除相同的種類至今共發(fā)現(xiàn)510余種不同的惡臭物質(zhì)[21,27-31]。不同畜禽類型的惡臭物質(zhì)種類也有所差異,牛場(chǎng)中惡臭物質(zhì)種類有70多種[27],雞場(chǎng)中有150 余種[32],豬場(chǎng)中高達(dá)500多種[28,31,33]。養(yǎng)殖場(chǎng)不同設(shè)施的惡臭物質(zhì)種類有所不同,畜禽糞便的堆積和處理設(shè)施中惡臭物質(zhì)種類最多,研究發(fā)現(xiàn)豬場(chǎng)糞便儲(chǔ)存設(shè)施的上部空氣中鑒定出295種惡臭物質(zhì)[28,34],糞便氧化塘污水中含有167種不同的惡臭物質(zhì)[31],禽舍內(nèi)部大約有100～150種惡臭物質(zhì)[29]。

畜禽惡臭成分復(fù)雜,主要包括揮發(fā)性脂肪酸(VFAs)、酚類(phenols)、醇類(alcohols)、醛類(aldehydes)、酮類(ketones)、酯類(esters)、醚類(ethers)、胺類(amines)、烴類(hydrocarbons)、鹵代烴類(halogenated hydrocarbons)、硫化物(sulphides)、含氮雜環(huán)化合物(nitrogen heterocycles)及芳香族化合物(aromatics)等有機(jī)成分[28,31,35-37]。各類VOCs包含具體不同的物質(zhì),可以進(jìn)一步分為次一級(jí)的亞類。除了有機(jī)成分外,惡臭物質(zhì)還包括氨氣、硫化氫等無機(jī)成分[38]。由于不同條件下形成的畜禽惡臭物質(zhì)復(fù)雜多樣,且在大氣中極易遷移轉(zhuǎn)化[39],因而目前關(guān)于各類惡臭物質(zhì)對(duì)畜禽惡臭的貢獻(xiàn)尚不完全清楚[40]。從已有研究來看,一般認(rèn)為畜禽惡臭中起關(guān)鍵作用的物質(zhì)主要是揮發(fā)性脂肪酸類,含硫化合物,芳香族化合物(主要是酚類和吲哚),以及氨和揮發(fā)性胺類4類[9,41-42]。

VFAs被認(rèn)為是畜禽惡臭物質(zhì)中最主要的組成[13,43]。大約60%的VFAs是乙酸[44],其次主要有丙酸、正丁酸、異丁酸、異戊酸、正癸酸、戊酸[45]。具有長碳鏈結(jié)構(gòu)的VFAs(C4～C9,如丁酸、戊酸、辛酸等)惡臭程度顯著高于短碳鏈結(jié)構(gòu)的VFAs(如乙酸和丙酸),其嗅閾值也較低[44]。由于在畜禽養(yǎng)殖中排放的VFAs大多是短碳鏈結(jié)構(gòu),故雖然檢測(cè)到的VFAs濃度很高,但一般也不會(huì)產(chǎn)生刺激性惡臭[42]。

含硫化合物一般具有強(qiáng)烈的刺激性惡臭氣味,是畜禽惡臭物質(zhì)的一個(gè)重要組成[38，46]。已經(jīng)鑒定出的最低嗅閾值的物質(zhì)中,有6種為含硫化合物[47]。含硫化合物主要有硫化氫、甲硫醇、丙硫醇、二甲基硫醚、二甲基二硫醚[31]。畜禽糞便中的硫大多以硫化氫和甲硫醇形式散發(fā)到空氣中[48],2種物質(zhì)占畜禽揮發(fā)性含硫惡臭物質(zhì)的70%～97%[49]。豬糞便揮發(fā)出的硫化氫質(zhì)量濃度達(dá)到90 μg·m-3[43],而豬舍空氣中甲硫醇質(zhì)量濃度達(dá)到3.6×104μg·m-3,是自身嗅閾值的947～120×106倍[50],因而甲硫醇被認(rèn)為是對(duì)畜禽惡臭貢獻(xiàn)最大的含硫化合物。通常情況下,含硫化合物濃度明顯高于VFAs,且含硫化合物嗅閾值低于VFAs,故一般認(rèn)為含硫化合物在惡臭中的作用要強(qiáng)于VFAs[21]。

畜禽惡臭物質(zhì)中的芳香族化合物主要是酚類和吲哚,具體包括苯酚、對(duì)甲酚、間甲酚、乙基苯酚、吲哚和甲基吲哚等[13]?？諝庵蟹宇悵舛容^高[31],研究發(fā)現(xiàn)豬舍空氣中對(duì)甲酚和苯酚分別占芳香族化合物的64%和26%,而吲哚和甲基吲哚濃度較低[13]。對(duì)甲酚不但其濃度要高于其他芳香族化合物,而且在芳香族化合物中其嗅閾值是最低的,因而相比于吲哚和苯酚,對(duì)甲酚是重要的惡臭物質(zhì)[51]。雖然畜禽惡臭物質(zhì)中苯酚濃度高于吲哚和甲基吲哚,但是其嗅閾值也高,同時(shí)苯酚具有芳香氣味,因而在該類物質(zhì)中,苯酚對(duì)惡臭貢獻(xiàn)度并不高[52]。

氨具有強(qiáng)烈的刺激性氣味,同時(shí)相比于其他惡臭成分,氨有相對(duì)較高的嗅閾值(0.3×10-6～53×10-6)[53],所以在早期研究中氨一度被認(rèn)為是表征畜禽惡臭的唯一指標(biāo)[40,54],至今許多國家還將氨作為惡臭評(píng)價(jià)的主要指標(biāo)[55]。但是,也有研究發(fā)現(xiàn)氨與惡臭之間并無顯著正相關(guān)關(guān)系[56-57]。畜禽養(yǎng)殖過程中散發(fā)的揮發(fā)性胺主要有甲胺、乙胺、三甲胺、尸胺和腐胺[58]。揮發(fā)性胺占揮發(fā)性氮化合物的比例很小,目前關(guān)于揮發(fā)性胺排放濃度測(cè)定研究還很少[21]。

從已鑒定出的惡臭物質(zhì)組成來看,惡臭物質(zhì)具有不同的相對(duì)分子質(zhì)量和分子結(jié)構(gòu),其沸點(diǎn)、蒸汽壓、水溶性和嗅閾值等理化性質(zhì)也不盡相同[59],因此各物質(zhì)在大氣中的反應(yīng)特性與環(huán)境行為也不同,在惡臭中的貢獻(xiàn)作用也存在差異。有研究[28]發(fā)現(xiàn),豬糞便排放的含有OH自由基的惡臭物質(zhì)中,68%在大氣中的存在時(shí)間短于24 h。CAI等[59]從環(huán)境毒性角度,將畜禽排放的50種VOCs分為9類,其中有5類為危險(xiǎn)大氣污染物。此外,不同畜禽類型產(chǎn)生惡臭成分不同,豬糞排放的臭氣物質(zhì)以揮發(fā)性低級(jí)脂肪酸類為主[14],雞糞的臭味成分以NH3、二甲基二硫和硫化氫為主[13,48],牛糞惡臭以低級(jí)脂肪酸為主[29]。

2 測(cè)定方法

目前畜禽惡臭的測(cè)定方法大致分為2類[60]:一是定量測(cè)定惡臭物質(zhì)組成的質(zhì)量濃度,即儀器分析法;二是通過嗅覺感受表征待測(cè)場(chǎng)所的惡臭程度,即嗅覺法。畜禽惡臭測(cè)定方法見圖1。

圖1 畜禽惡臭主要測(cè)定方法Fig.1 Main methods for measurement of odor in animal production

2.1 儀器分析法

儀器分析法主要用于測(cè)定單一的惡臭物質(zhì),包括實(shí)驗(yàn)室儀器分析法和自動(dòng)監(jiān)測(cè)儀器法2類。實(shí)驗(yàn)室儀器分析法主要有氣相色譜(GC)法、氣相色譜質(zhì)譜聯(lián)用(GC-MS)法、高效液相色譜(HPLC)法、質(zhì)子傳遞反應(yīng)質(zhì)譜儀(PTR-MS)[61]、分光光度法(紫外-可見分光光度法)等。實(shí)驗(yàn)室儀器分析法在測(cè)定惡臭物質(zhì)種類和濃度方面發(fā)揮重要作用,針對(duì)惡臭物質(zhì)的樣品前處理和主要分析方法已有較為全面的綜述[62],在此不再贅述。隨著監(jiān)測(cè)技術(shù)的發(fā)展,由于自動(dòng)監(jiān)測(cè)儀器法可以連續(xù)和自動(dòng)監(jiān)測(cè)畜禽惡臭物質(zhì)的排放情況,在惡臭物質(zhì)排放機(jī)理研究和惡臭管理方面發(fā)揮的作用越來越突出。自動(dòng)監(jiān)測(cè)儀器法主要包括氣體探測(cè)管、接觸式傳感器法和光學(xué)方法[63]。表1列出了常用畜禽惡臭自動(dòng)監(jiān)測(cè)方法[64-89]。

表1常用畜禽惡臭自動(dòng)監(jiān)測(cè)方法

Table1Summaryofautomaticmonitoringandanalysismethodsforodorinanimalproduction

方法原理常測(cè)畜禽惡臭物質(zhì)優(yōu)點(diǎn)缺點(diǎn)參考文獻(xiàn)氣體探測(cè)管法利用被測(cè)氣體成分附著在固體指示劑表面的顯色反應(yīng)來測(cè)定氣體濃度NH3、H2S、CO2、二甲基硫醚使用方便檢測(cè)精度較低[64-67]接觸式傳感器法 半導(dǎo)體傳感器以半導(dǎo)體材料與氣體接觸后所產(chǎn)生的性質(zhì)變化表征待測(cè)氣體濃度與成分NH3、H2S操作簡(jiǎn)單,對(duì)氣體具有一定的選擇性,成本較低穩(wěn)定性較差,受環(huán)境影響較大[68] 電化學(xué)傳感器利用物質(zhì)的氧化還原特性,通過測(cè)量待測(cè)物質(zhì)與電極的電化學(xué)反應(yīng)所釋放的電流大小來測(cè)量氣體濃度NH3、H2S具有良好的氣體選擇性,檢測(cè)精度高不宜長時(shí)間使用,需要定期進(jìn)行校準(zhǔn),且使用壽命短[69-72] 電子鼻主要由傳感器陣列和智能算法組成,通過模式識(shí)別模擬人的嗅覺NH3、H2S、二甲基硫醚與人工嗅覺法相比,電子鼻更加穩(wěn)定所用的傳感器陣列數(shù)目多且復(fù)雜,成本昂貴[73-76]光學(xué)方法 非分光紅外光譜利用化合物分子對(duì)紅外光具有吸收作用、通過在紅外光譜上形成吸收譜線來鑒別氣體濃度NH3、H2S、CO、N2O、CH4方法成熟,檢測(cè)精度較高信噪比較低,無法進(jìn)行開放光程測(cè)定[77-79] 紫外差分吸收光譜利用空氣中分子的紫外可見譜區(qū)的窄帶特性來鑒別氣體成分,并根據(jù)吸收強(qiáng)度反演氣體濃度NH3、氮氧化物、碳氧化物開放光程測(cè)定,檢測(cè)精度高,可以達(dá)到10-9數(shù)量級(jí)氣體選擇性不高[80-82] 傅里葉變換紅外光譜利用干涉儀對(duì)光源發(fā)出的光進(jìn)行調(diào)制,對(duì)接受到的干涉圖樣進(jìn)行傅里葉變換,得到被待測(cè)氣體吸收后的光譜圖,經(jīng)光譜圖分析后得到待測(cè)氣體濃度NH3、N2O、CO、CH4能夠?qū)崿F(xiàn)對(duì)畜禽生產(chǎn)場(chǎng)所區(qū)域氣體分布的監(jiān)測(cè)價(jià)格昂貴且體積巨大[83-86] 可調(diào)諧激光光譜激光器發(fā)出的經(jīng)調(diào)制的單色光通過待測(cè)氣體后由探測(cè)器接收,并提取其中的諧波信號(hào),利用諧波信號(hào)的強(qiáng)度反演待測(cè)氣體濃度NH3、N2O、CH4可獲取氣體空間分布情況,小型化,操作更簡(jiǎn)單,成本低每次只能進(jìn)行1種氣體成分的檢測(cè)[87-89]

綜合現(xiàn)有惡臭測(cè)定方法,目前還無理想的畜禽惡臭測(cè)定方法。儀器分析法在惡臭物質(zhì)鑒定與某些關(guān)鍵惡臭物質(zhì)的監(jiān)測(cè)方面有一定優(yōu)勢(shì)。從環(huán)境管理角度來看,自動(dòng)監(jiān)測(cè)技術(shù)具有非常好的應(yīng)用前景。近年來,電子鼻技術(shù)在不斷的發(fā)展,隨著系統(tǒng)簡(jiǎn)化和成本降低,會(huì)逐漸成為接觸式傳感器技術(shù)的一個(gè)主要發(fā)展方向。光學(xué)方法由于其成本較高,操作復(fù)雜,故很難推廣。但是,開放光程技術(shù)在養(yǎng)殖場(chǎng)尺度上針對(duì)某些惡臭物質(zhì)的高分辨時(shí)空測(cè)定還是有很好的應(yīng)用前景。

2.2 嗅覺法

嗅覺法是利用人類的鼻子作為傳感器,對(duì)具有氣味的氣體成分和濃度進(jìn)行測(cè)量的方法,實(shí)質(zhì)上是對(duì)待測(cè)場(chǎng)所惡臭的一個(gè)綜合判斷[7]。嗅覺法分為直接法和稀釋法2種。

2.2.1直接法

直接法是一種定性方法,直接通過嗅覺感知的惡臭感覺對(duì)照惡臭強(qiáng)度分級(jí)判定惡臭程度,即用數(shù)字等級(jí)或語言描述表示臭氣強(qiáng)弱。目前,國內(nèi)外惡臭等級(jí)的分級(jí)方法很多,大致有3種分級(jí)方法:語言描述分級(jí)法、數(shù)值估量法、參考惡臭等級(jí)分級(jí)法[90]。其中,語言描述分級(jí)法較為常用,我國目前推薦的惡臭等級(jí)即為語言描述分級(jí)法,采用的是6級(jí)分類。數(shù)值估量法因誤差較大而很少使用。參考惡臭等級(jí)分級(jí)法根據(jù)實(shí)際情況選擇合適的惡臭等級(jí)參考范圍。歐洲采用不同濃度的正丁醇水溶液或稀釋氣體惡臭程度表征惡臭等級(jí),通過對(duì)樣品進(jìn)行嗅辨判定,得出相應(yīng)的惡臭等級(jí)[91]。由于在高惡臭強(qiáng)度時(shí)很難區(qū)分其等級(jí),如果要將此分級(jí)方法運(yùn)用于畜禽養(yǎng)殖場(chǎng)這種特殊環(huán)境,還需要對(duì)其分級(jí)描述進(jìn)行改善[92]。

2.2.2稀釋法

稀釋法是一種相對(duì)定量方法,是指用無臭空氣對(duì)某一惡臭樣品進(jìn)行連續(xù)稀釋,直至達(dá)到無臭狀態(tài)。根據(jù)稀釋方法分為靜態(tài)稀釋法和動(dòng)態(tài)稀釋法。靜態(tài)稀釋法主要包括無臭室法、注射器法和三點(diǎn)比較式臭袋法。無臭室法測(cè)試精度高,但設(shè)備造價(jià)很高且不便于現(xiàn)場(chǎng)測(cè)定。注射器法操作簡(jiǎn)便,但精度不高,且注射器體積有限,難以配制出高稀釋倍數(shù)的試樣。三點(diǎn)比較式臭袋法是目前最為常用的分析方法。這種方法的測(cè)量精度相對(duì)較高,測(cè)量的重復(fù)性和再現(xiàn)性好,嗅辨員個(gè)體之間的誤差小。我國的GB/T 14675—93《空氣質(zhì)量 惡臭的測(cè)定 三點(diǎn)比較式臭袋法》就是基于三點(diǎn)比較式臭袋法制定的。汪開英等[93]運(yùn)用靜態(tài)稀釋法研究了不同類型地面結(jié)構(gòu)的育肥豬舍惡臭濃度與惡臭排放系數(shù)。

動(dòng)態(tài)稀釋法是使用儀器設(shè)備對(duì)臭氣樣品進(jìn)行連續(xù)稀釋后供人嗅辨的方法。動(dòng)態(tài)嗅覺儀使用微電腦控制自動(dòng)完成樣品定比稀釋,提高了稀釋效率,同時(shí)提高了稀釋精度和重復(fù)精度[94]。歐洲標(biāo)準(zhǔn)CSN EN 13725對(duì)于動(dòng)態(tài)嗅覺儀的使用進(jìn)行了詳細(xì)規(guī)定,澳大利亞、新西蘭和美國都依據(jù)此標(biāo)準(zhǔn)形成本國的標(biāo)準(zhǔn)[7,90]。國外關(guān)于畜禽養(yǎng)殖惡臭的研究多基于動(dòng)態(tài)嗅覺計(jì)技術(shù)開展[32, 95-96]。

但是,嗅覺法同樣存在很多不足。嗅覺法極易受到嗅辨員自身因素的影響,測(cè)量結(jié)果的精度較低[61]。該方法需要采樣并與嗅覺專家小組配合,導(dǎo)致測(cè)定成本較高[97]。嗅覺法只能進(jìn)行間斷測(cè)定,且通常在實(shí)驗(yàn)室內(nèi)完成,測(cè)量并不具備實(shí)時(shí)性,無法實(shí)現(xiàn)對(duì)畜禽惡臭的實(shí)時(shí)監(jiān)測(cè)[98]。此外,該方法在采樣、保存樣品以及稀釋過程中會(huì)出現(xiàn)惡臭物質(zhì)損耗的現(xiàn)象[99-101],導(dǎo)致測(cè)定精度降低。而許多情況下,畜禽養(yǎng)殖環(huán)境中惡臭物質(zhì)濃度很低,因而限制了該方法的運(yùn)用。

3 畜禽惡臭表征與評(píng)估

3.1 惡臭表征

所謂惡臭濃度(odor concentration,OC,Co)是剛剛稀釋到無臭時(shí)所需的稀釋倍數(shù),并非惡臭的物質(zhì)濃度[7]。Co無量綱,通常也寫作惡臭單位(odor unit,OU)。歐洲標(biāo)準(zhǔn)中采用每立方米空氣中惡臭的單位數(shù)(OU·m-3)表示Co。實(shí)質(zhì)上,Co是樣品稀釋到閾值濃度的稀釋倍數(shù),故可以根據(jù)某一具體惡臭物質(zhì)的實(shí)測(cè)濃度與閾值濃度的比值計(jì)算Co值。Co計(jì)算公式為

(1)

(2)

式(1)～(2)中,Co為惡臭濃度,OU·m-3;Vo為惡臭樣品體積,L;Va為無臭空氣體積,L;ρo為某惡臭物質(zhì)實(shí)測(cè)濃度,μg·m-3;ρd為某惡臭物質(zhì)閾值濃度,μg·m-3。為了便于比較,在歐洲標(biāo)準(zhǔn)CSN EN 13725中,規(guī)定1 OU·m-3相當(dāng)于123 μg正丁醇在1 m3無味氣體中產(chǎn)生的氣味濃度,即相當(dāng)于0.040 μL·L-1正丁醇的嗅閾值濃度[7]。

在測(cè)量畜禽惡臭排放時(shí),通常將Co與通風(fēng)速率(Q,m3·s-1)相乘得到排放系數(shù)(E,OU·s-1)[102]。

由于惡臭濃度數(shù)值有時(shí)很大,不易與惡臭給人的感覺聯(lián)系起來,目前也常用惡臭強(qiáng)度(odor intensity,OI,Io)表示惡臭污染的程度。Io可用韋伯-費(fèi)希納公式(Weber-Fechner公式)來表示:

Io=10lgCo。

(3)

但用式(3)計(jì)算常出現(xiàn)較大誤差,如Co=1時(shí)，Io=0,顯然與事實(shí)不符。因此,式(3)應(yīng)修正為

Io=10algCo+b。

(4)

式(4)中,a、b為常數(shù)。

3.2 惡臭評(píng)估

惡臭是通過嗅覺產(chǎn)生的一種心理感受,由于畜禽惡臭物質(zhì)成分復(fù)雜,且各種氣體散發(fā)出的臭味相互干擾而并非簡(jiǎn)單疊加,這給惡臭的評(píng)估帶來了難度。因此,到目前為止,尚沒有一種十分理想的惡臭評(píng)估方法[98]。有學(xué)者通過儀器測(cè)定某種(如硫化氫[41])或某一類惡臭物質(zhì)(如VAFs[44])的釋放速率和環(huán)境中的濃度,以此來進(jìn)行惡臭評(píng)估。因?yàn)閻撼敉ǔ６际怯啥喾N惡臭物質(zhì)混合形成的,僅僅依靠對(duì)其中幾種惡臭物質(zhì)的測(cè)定無法衡量其整體上給人帶來厭惡感的程度[55]。嗅覺法可以直接表征對(duì)惡臭的心理感受程度,亦可以通過惡臭濃度和惡臭指數(shù)半定量地表征畜禽惡臭。與許多國家一樣，我國也采用嗅覺測(cè)定法來判別惡臭的綜合污染程度[55,93]?？梢?嗅覺法是目前主流的惡臭評(píng)估方法。

但是,如2.2節(jié)所述該方法也存在不可控制的測(cè)定誤差?？梢?目前畜禽惡臭的評(píng)估面臨2個(gè)方面的挑戰(zhàn):一方面，全部測(cè)定惡臭物質(zhì)存在技術(shù)和成本的制約,另一方面，主觀表征存在不可避免的誤差。面對(duì)畜禽惡臭評(píng)估存在的挑戰(zhàn),現(xiàn)在有學(xué)者在致力于構(gòu)建惡臭具體成分物質(zhì)的質(zhì)量濃度與OC或OI之間的定量關(guān)系,即將測(cè)定畜禽惡臭物質(zhì)濃度轉(zhuǎn)變?yōu)闇y(cè)定惡臭濃度或惡臭強(qiáng)度[98]。

在相關(guān)研究中,借鑒食品學(xué)中關(guān)于惡臭活性值(odor activity value,OAV,VOA)的方法對(duì)畜禽惡臭進(jìn)行評(píng)估成為一個(gè)研究熱點(diǎn)[103]。所謂的OAV即某種物質(zhì)實(shí)測(cè)濃度與嗅閾值的比值,可以采用式(1)～(2)進(jìn)行計(jì)算;若是多種惡臭物質(zhì),則將各測(cè)定物質(zhì)的OAV累加得到惡臭活性值之和(sum of the odor activity value,SOAV)[104]。從概念上來理解,OAV值越大的物質(zhì)對(duì)惡臭的貢獻(xiàn)就越大,通過比較各物質(zhì)的OAV值,可以判別畜禽惡臭的主要貢獻(xiàn)物質(zhì)[105]。BLAZY等[106]通過測(cè)定生豬屠宰場(chǎng)豬糞中的66種惡臭物質(zhì)濃度來計(jì)算各惡臭物質(zhì)的OAV,發(fā)現(xiàn)三甲胺、硫化氫和甲硫醇是產(chǎn)生惡臭的主要物質(zhì)。PARKER等[107]通過計(jì)算豬場(chǎng)和牛場(chǎng)20種惡臭物質(zhì)的OAV,發(fā)現(xiàn)硫化氫、對(duì)甲酚、異戊酸、氨氣和二乙基二硫醚為豬場(chǎng)惡臭的主要貢獻(xiàn)物,而硫化氫、對(duì)甲酚、丁酸和異戊酸為牛場(chǎng)惡臭的主要貢獻(xiàn)物。通過擬合OAV和OC的關(guān)系,發(fā)現(xiàn)運(yùn)用SOAV擬合的結(jié)果會(huì)低估惡臭濃度2～3倍[107],而VOA,max可以更好地確定化學(xué)組成與OC的關(guān)系[106]。但是,OAV法還是需要通過嗅覺法來測(cè)定OC值,而無法避免人為主觀因素的影響。WU等[108]對(duì)該方法做了改進(jìn),無需通過嗅覺法來同步測(cè)定OC值,客觀地實(shí)現(xiàn)惡臭物質(zhì)濃度向OC或OI的轉(zhuǎn)變,取得了很好的擬合效果。

4 總結(jié)與展望

自20世紀(jì)60年代以來,關(guān)于畜禽養(yǎng)殖中惡臭物質(zhì)的鑒定已經(jīng)取得了長足進(jìn)步。歐美已經(jīng)有了大量關(guān)于畜禽惡臭的研究報(bào)道,亞洲的日本和韓國的相關(guān)研究也陸續(xù)開展。我國開展畜禽惡臭方面的研究起步較晚,多見于20世紀(jì)90年代。

隨著測(cè)試技術(shù)的發(fā)展,對(duì)畜禽惡臭物質(zhì)成分的鑒定已經(jīng)有了相當(dāng)?shù)姆e累,為進(jìn)一步進(jìn)行惡臭評(píng)估、惡臭管控提供了一定理論支撐。總的來看,學(xué)者對(duì)惡臭物質(zhì)的鑒定投入了很大精力,發(fā)現(xiàn)了越來越多的畜禽惡臭物質(zhì)組成成分,發(fā)現(xiàn)的惡臭物質(zhì)種類逐漸增加。研究更多關(guān)注于測(cè)定各惡臭源釋放出的惡臭物質(zhì)成分和種類,對(duì)于各惡臭物質(zhì)在畜禽環(huán)境中的相互作用過程、各物質(zhì)在惡臭中的貢獻(xiàn)作用及關(guān)鍵惡臭物質(zhì)的識(shí)別還顯得不足。同時(shí),對(duì)于關(guān)鍵惡臭物質(zhì)的環(huán)境行為與影響機(jī)制研究,多是基于溫室氣體的研究需要開展的。從畜禽類型來看,對(duì)豬場(chǎng)惡臭的研究明顯多于牛場(chǎng)和雞場(chǎng)等其他養(yǎng)殖類型。從惡臭來源來看,多數(shù)研究集中于畜禽場(chǎng)所的環(huán)境空氣,對(duì)于糞便儲(chǔ)存、處理設(shè)施上方空氣及空氣中的懸浮顆粒物研究還相對(duì)較少。此外,目前多單獨(dú)研究禽舍、糞便處理設(shè)施或還田過程,缺少針對(duì)整個(gè)養(yǎng)殖場(chǎng)各惡臭排污節(jié)點(diǎn)的整體研究,也無基于養(yǎng)殖場(chǎng)尺度的惡臭物質(zhì)組成特征的系統(tǒng)研究。

實(shí)現(xiàn)連續(xù)、高精度惡臭監(jiān)測(cè)是目前惡臭測(cè)定技術(shù)發(fā)展的主要方向。從環(huán)境管理角度來看,嗅覺法在綜合評(píng)判惡臭污染程度方面具有一定優(yōu)勢(shì)。嗅覺儀與分析儀器結(jié)合使用是嗅覺法發(fā)展的一個(gè)主要趨勢(shì)。在測(cè)定惡臭物質(zhì)的基礎(chǔ)上,對(duì)惡臭進(jìn)行科學(xué)評(píng)估是進(jìn)行畜禽惡臭控制與管理的基礎(chǔ)。但是,目前畜禽惡臭的評(píng)估方法多源于食品學(xué)惡臭的相關(guān)評(píng)估技術(shù)方法。為了統(tǒng)一畜禽惡臭管理標(biāo)準(zhǔn),同時(shí)能在實(shí)際中盡量減少惡臭評(píng)估工作量,在目前的技術(shù)條件下,將測(cè)定畜禽惡臭物質(zhì)濃度客觀地轉(zhuǎn)變?yōu)闇y(cè)定惡臭強(qiáng)度是畜禽惡臭評(píng)估中亟待解決的關(guān)鍵問題。

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AReviewofResearchesonComposition,MeasurementandAssessmentofOdorantsinLivestockandPoultryBreeding.

LIU Bo1, WANG Wen-lin2, LIU Xiao1, FAN Zhou2, YANG Wan-jing1, XU Qiao1, GUAN Lei1, ZENG Jie-liang1, LI Wen-jing2， HE Fei2

(1.School of Geography Science, Nantong University, Nantong 226007, China; 2.Nanjing Institute of Environmental Sciences, Ministry of Environmental Protection, Nanjing 210042, China)

With rapid development of the livestock and poultry breeding industry in China, odor from the industry has become a main environment issue that not only arouses complaints from nearby residents and disputes between the residents and the industry, but also seriously restrains sustainable development of the industry. It is, therefore, essential to determine sources and composition of the odor and sum up techniques or methods to determine, characterize and evaluate the odor, which is of great significance to scientific assessment of hazard of the odor and designing of control measures. In this review, compositions and characteristics of the odorants from the industry were collated, main techniques to measure odor compared for advantage and disadvantage, and chief methods to characterize and assess odor discussed. Volatile fatty acids (VFAs), sulfocompound, aromatics (phenols and benzpyrole) as well as ammonia and volatile amine are the key substances in odor from the industry. Methods to determine the odor can be roughly sorted into two types, instrumental and olfactory, of which each has its own advantages and disadvantages. Based on analysis of compositions of the odorants available, key components of the odor from the industry are identified, and continuous in-situ monitoring of odor will be the focus for researches in future. Moreover, as the composition of odor is very complicated, establishment of a reasonable relationship model for mutual conversion between odor concentration and odor intensity may be a workable approach to quantitative evaluation of odor.

livestock and poultry breeding; odorant; measurement technique; assessment method

2017-02-04

環(huán)保公益性行業(yè)科研專項(xiàng)(201509038); 環(huán)境保護(hù)部部門預(yù)算項(xiàng)目(2110107); 江蘇省自然科學(xué)基金(BK20131201); 江蘇省大學(xué)生創(chuàng)新訓(xùn)練計(jì)劃(201610304038Z,2016114); 中央級(jí)公益性科研院所基本科研業(yè)務(wù)專項(xiàng)

① 通信作者E-mail: 175729057@qq.com

X512

A

1673-4831(2017)10-0872-10

10.11934/j.issn.1673-4831.2017.10.002

劉波(1976—),男,江蘇連云港人,副教授,博士,從事環(huán)境面源污染過程與防治研究。E-mail: lb@ntu.edu.cn

責(zé)任編輯： 李祥敏)