畜禽養殖糞水酸化貯存及氮素減損增效研究進展

張冬麗，張朋月，沈玉君，丁京濤

畜禽養殖糞水酸化貯存及氮素減損增效研究進展

張冬麗，張朋月，沈玉君，丁京濤※

（1. 農業農村部規劃設計研究院農村能源與環保研究所，北京 100125；2. 農業農村部資源循環利用技術與模式綜合性重點實驗室，北京 100125）

畜禽糞水酸化貯存能夠有效調控糞水貯存中微生物、環境與氮素間的作用關系，實現糞水氮素的減損增效，是一種具有廣泛應用前景的關鍵技術。該研究系統綜述了糞水酸化貯存中氮素的遷移轉化機理，比較評價了常見酸化劑和不同酸化貯存工藝的應用效果，分析了酸化貯存技術對糞水氮素減損增效的影響。梳理總結得到：糞水酸化存儲中氮素的遷移轉化機制主要包括有機氮礦化、銨態氮固持、無機氮轉化的抑制及硝化3個關鍵環節，可以依靠改變微生物作用和化學平衡狀態實現氮素的減損；與其他酸化工藝相比，長期酸化工藝具有酸化效果更加穩定、應用范圍較為廣泛等優勢；糞水酸化技術能夠大幅降低NH3排放，以及部分N2O的排放，進而提高糞肥還田后土壤肥效，但不合理的酸化貯存技術及施用方式也會降低糞水肥效，甚至引起二次污染；未來應重點從氮素遷移轉化路徑的定量分析、復合酸化劑的開發、糞肥施用效果及風險的評估應對等方面進行深入研究。

酸；肥效；畜禽糞水；氮素減損

0 引 言

隨著畜禽養殖業規?；陌l展，糞水處理成為限制養殖場發展的重要因素[1]，相對固體糞便而言，液態糞水處理難度大，更易導致環境污染。據統計，中國畜禽養殖糞污年產生量約30.5億t，其中養殖過程產生的糞水量大、分散，更容易導致面源污染[2]。目前，貯存發酵被認為是一種實現養殖糞水無害化、資源化的處理方式，能夠利用糞水中的氮、磷、鉀等元素，同時對部分有害微生物進行滅活，既能促進物質循環又能提升廢棄污染物的經濟價值[3]。然而，在傳統的糞水貯存發酵工藝中，容易產生氨氣（NH3）、硫化氫（H2S）等臭氣以及氧化亞氮（N2O）、甲烷（CH4）等溫室氣體，不僅造成糞肥產品肥效的降低，還會造成PM2.5濃度上升等一系列環境問題[4-6]。

近年來，隨著畜禽糞水排放規模的進一步增大以及生態環境保護要求的持續提高，糞水酸化技術逐漸成為糞污臭氣控制研究和應用的關鍵技術[7-9]。畜禽糞水酸化貯存技術能夠通過改變糞水pH值，實現系統中NH4+和NH3間平衡關系的調節，進而減少糞水貯存及農田施用中氨氣等氣體排放，提高糞水貯存中養分固持率[10-12]。糞水酸化貯存技術已在國外得到較多的發展和應用，例如以濃硫酸酸化貯存糞水技術已在丹麥、瑞典等國普遍推廣，丹麥有12%～20%的糞水采用酸化處理[13-14]。

在2021年8月全國畜牧總站印發的《規范畜禽糞污處理降低養分損失技術指導意見》中，糞水酸化技術已成為治理糞污氨揮發的主推技術，同時也被納入《“十四五”全國畜禽糞肥利用種養結合建設規劃》。但總體來看，中國對于糞水酸化貯存的研究尚處于起步階段，有待進一步系統、深入研究。本文系統闡述了當前畜禽養殖糞水酸化貯存技術研究進展，并展望了其應用前景，以期為中國畜禽養殖糞水資源化、無害化利用技術研發應用提供理論和數據支撐。

1 糞水酸化貯存中的氮素遷移及其減損特征

1.1 糞水酸化貯存中的氮素遷移

糞水是糞便與尿液的混合物，含有豐富的氮素等養分（見表1）[15-18]，適宜在經過貯存發酵后還田進行資源化利用。然而，糞水中的尿酸、尿素以及未分解的蛋白質等氮素載體在好氧降解、水解或礦化作用下使糞水含有大量銨態氮，極易釋放出NH3，造成氮素養分的損失，成為限制養殖糞水資源化利用的難點之一[19–22]。在糞水酸化貯存過程中，氮循環在很大程度上依賴復雜的化學生物作用。糞水中氮素的形態以有機氮和銨態氮為主，其總和占糞水中總氮質量分數的97%以上。因此，分析其氮素遷移機制，主要可以歸納為有機氮的礦化、銨態氮的固持、無機氮轉化的抑制及硝化3個關鍵環節（見圖1）。

表1 養殖糞水中主要物質含量

1）有機氮的礦化。向糞水中添加酸化劑后，少量硫酸分解了糞水底泥中部分大顆粒有機物，使之懸浮于糞水中提高了糞水中有機氮的含量。在酸性條件下，糞水中的有機氮通過好氧/厭氧微生物的礦化作用向銨態氮轉化，另一部分有機氮則通過水解作用轉化為氨基酸，并在脫氨基的作用下生成銨態氮[23-24]。2）銨態氮的固持。酸化工藝作用下，硫酸等酸化劑與銨態氮結合生成能夠長期穩定固持的銨鹽。3）無機氮轉化的抑制及硝化。有研究表明[25-27]，糞水酸化能夠有效抑制糞水中微生物活性，通過濃硫酸酸化后糞水中耗氧率、硫酸鹽還原率均明顯降低，這可能是由于酸化糞水中含有高濃度的短鏈揮發性脂肪酸，它們作為細胞膜電位的解耦劑，抑制了微生物的代謝。因此，酸化抑制了有機氮向無機氮素的轉化，微生物活性的降低使得糞水中存在一定量過剩的溶解氧，這部分溶解氧被硝化細菌利用，也使得糞水中硝態氮含量逐漸升高，亞硝態氮含量不斷降低。

圖1 畜禽養殖糞水酸化貯存及其氮素減損增效示意圖

1.2 糞水酸化貯存的氮素減損路徑

糞水酸化貯存中氮素的損失途徑主要是NH3的產生和散逸。糞水為微生物提供了一種復雜的環境條件，不僅具有好氧微生物所需的環境，同時亦為厭氧微生物提供了所需的生存環境，因此，結合糞水酸化貯存中的氮素遷移機制的相關研究結論，糞水中氮素形態轉化及氮素損失的調節，主要是通過改變微生物作用和化學平衡狀態來實現。其分別對應了2種氮素減損的技術路徑，一是添加酸化劑降低糞水pH值以改變糞水中NH4+與NH3的動態平衡，促進NH4+生成，以減少糞水中溶解NH3的排放；二是通過降低糞水pH值使微生物活性下降，降低糞水中有機物的礦化作用，進而減少NH3的產生及排放[28]。

1.3 糞水酸化貯存與傳統工藝的差異

與傳統糞水貯存發酵工藝相比，糞水酸化貯存能夠穩定固持糞水中的NH4+，體現了氮素減損的比較優勢[29]。在傳統養殖糞水貯存發酵工藝中，糞水一般是以自然靜置貯存為主，表層糞水以好氧發酵為主，但深層糞水則以厭氧發酵為主。而在糞水酸化貯存發酵中，酸化后的糞水所提供的效應離子不會被降解及轉化（易分解有機物及硝酸除外），能夠穩定的固持糞水中的NH4+，使糞水中被固持的NH4+長期的貯存于糞水中（圖2）。

圖2 糞水酸化貯存與傳統工藝對比示意圖

綜合已有研究[21-29]，雖然酸化糞水一定程度上抑制了糞水中微生物對含氮有機物的礦化作用，但其也使氮素固持效率有了顯著提高，進而減少氮素損失和氨氣排放。酸化環境下一定量過剩溶解氧促進糞水中微生物的硝化作用，使糞水中硝態氮含量升高?？偟膩砜?，酸化技術使糞水貯存中總氮、銨態氮、硝態氮含量升高，氨氣排放、亞硝態氮含量降低，故酸化糞水對提高糞水養分固持率，減少環境污染具有重要意義。

2 不同糞水酸化貯存工藝的比較評價

2.1 不同類型酸化劑

糞水酸化劑目前主要有3種類型[10,30]。第一種是強酸類，主要有濃H2SO4、HNO3和H3PO4等，其中濃H2SO4以其低廉的價格應用最廣，強酸酸化劑用量少，但糞水酸化后pH穩定性差，且酸類具腐蝕性，對設備和安全操作要求較高，其作用方式為酸與糞水中的銨水反應生成相對更穩定的銨鹽和水，降低了銨氮向氨氣的轉化。其中硫酸以價格便宜，用量少等優勢可用于中國農村糞水的酸化。但其購置、存儲、管理過程繁瑣，故建議在農村地區推廣以磷酸為主的酸化劑。

第二種是水解呈酸性的鹽類，主要有明礬、過磷酸鈣、氯化鋁、硫酸鋁等物質。此類酸化劑水解后一般生成堿性沉淀物與酸，酸與氨水反應生成銨鹽和水，此類酸化劑酸化效果相對較穩定，但投加量相對酸類酸化劑較多，其應用經濟效益及環境效益是該工藝的主要考量因素[9]。

第三種是易分解有機物，目前以葡萄糖和蔗糖研究較多[10,31]。這類物質主要是通過向糞水中投入大量的易分解有機物，促進微生物快速增長，待糞水中的溶解氧不足以供給微生物進行呼吸作用時，糞水中的厭氧微生物大量繁殖，厭氧的呼吸作用將有機物分解為乳酸，通過乳酸與氨水反應生成乳酸銨和水。在糞水貯存后期，隨著易分解有機物的厭氧降解，糞水中的有機酸會逐漸轉化為甲烷，失去酸化效果。此方法投入量較大，成本偏高，會產生酸性臭氣，并吸引蛾蠓等飛蟲，引發二次污染，實際應用較少。

2.2 不同類型酸化方式

按照酸化場所，糞水酸化方式主要有養殖舍內長期酸化、貯存池中長期酸化和施用時短期酸化3種方式[10,32-33]。糞水酸化施用方式對酸化存儲過程中氮素損失量影響顯著[34-35]。

1）養殖舍內長期酸化是指糞水在養殖舍內酸化后，隨糞溝流入酸化處理罐，再添加酸化劑，進行酸化，同時增加曝氣并不斷攪拌以減少酸化過程中氣泡的產生，酸化后的糞水一部分回流至養殖舍，一部分進入糞水儲罐或糞水貯藏池。此方法的優點在于糞水酸化后有利于進行固液分離，同時收集的糞水能夠在貯存及施用過程中的各個階段均能起到減少NH3的揮發作用，進入貯存設施的糞水一般不再進行酸化，進入養殖舍收集系統的糞水會注入新的糞水，并再次進入酸化系統酸化，如此循環可使酸化效果更穩定，此種酸化技術目前應用最廣；2）貯存池中長期酸化是指糞水在貯存池中進行酸化，向貯存池中投入酸化劑并輔以不斷攪拌。此方法在酸化過程中會產生大量的氣泡，增加管理風險，另外，如果貯存時間較長，為了防止氨揮發作用增強，需要根據情況再次酸化；3）施用時短期酸化是指在糞水農田施用之前，向施肥罐車中添加酸化劑，通過罐車攪拌機混合均勻進行酸化，主要降低糞水還田施用階段NH3的揮發，提高氮素利用率[36]。

3 酸化貯存對糞水氮素減損增效影響

3.1 對氨氣排放的影響

糞水酸化能夠有效抑制糞水的堿性環境以及其中的微生物活性[25]，同時滅活糞水中部分有害微生物及致病菌[17]，從而通過化學生物作用降低NH3的排放。研究表明糞水酸化可以降低15%～77%的NH3排放（見表2），其中沈玉君等[37]研究成果表明酸化牛糞水至pH值為6.0可減少糞水貯存初始階段31.3%～54.0%的氨氣排放；DAI[38]等利用硫酸（H2SO4）酸化技術，可減少豬場污水和牛糞水50%以上的NH3排放。

酸化貯存對糞水氮素減損效果與酸化劑用量和酸化劑類型等因素密切相關[39]。郜斌斌等[12,40]的研究亦表明糞水酸化可大幅降低糞水中的NH3排放，同時NH3的排放隨酸化pH的降低而不斷降低；REGUEIRO等[41]研究發現在糞水中添加明礬也能起到類似的的減排效果，同時也能促進磷（P）的增溶、提效，但其作用效果弱于常見強酸酸化劑。然而，目前大部分酸化糞水的pH值通常會控制在5.1以上，以使糞水酸化后酸堿度能夠逐漸恢復至中性或弱堿性。主要原因是當酸化pH值過低時，可能會導致糞水長期貯存后仍呈酸性，不利于后期的還田利用，也增加了酸化工藝成本[42]。

表2 糞水酸化后氨氣排放情況

3.2 對N2O氣體排放的影響

糞水酸化貯存中，N2O主要來自氮素降解過程的反硝化階段，已有研究[37]表明，酸化會抑制糞水中有機物的降解，故理論而言酸化后的糞水在貯存中含氮有機物的降解率會下降，導致糞水中的銨氮生成量下降，且酸化劑的加入會降低銨氮向硝氮的轉化率，從而進一步降低硝氮向N2O的轉化，故酸化糞水理論上也會顯著抑制糞水中N2O的排放量[43-46]。HUSTED以及WANG等學者[39-40]的研究均表明，糞水酸化會顯著降低酸化糞水貯存期間CH4、N2O等溫室氣體的排放量，雖然在糞水酸化階段排放量會顯著升高，主要是由于酸化階段攪拌擾動糞水導致的，并非添加酸化劑導致的。此外，李路路等[42,47]的研究表明酸化糞水會抑制N2O的排放，同時李路路還發現酸化沼液會提升2.59倍，但酸化沼液對CO2的排放量計劃無影響。綜上酸化糞水可以有效降低糞水貯存期間溫室氣體的排放。

3.3 對糞肥還田后土壤肥效的影響

國內外已有研究發現，糞水酸化后還田可以提高土壤中N、P等有效態養分含量，對作物生長具有重要意義（見表3）。酸化糞污不僅可以降低貯存期糞污中氨氣的排放[28]，提高糞水中無機鹽成分，在酸化糞污施用到農田后也能夠有效提高作物產量。FANGUEIRO等[48]通過向具有高有機質含量的石灰性壤土和低有機質含量的酸性砂土中施入酸化的糞污，土壤中的NH4+在施入后的30 d內明顯大于添加未酸化糞污的處理，可以看出施入酸化處理的糞污可以使土壤中的N以NH4+的形式停留在土壤中，降低土壤中NH3揮發的損失。S?RENSEN[13,49]等的研究也表明向農田施入酸化后的糞污能夠明顯降低土壤中NH3的揮發，同時其表明施入酸化的糞污的農田中CH4的累積排放量也顯著下降，FROST等[50]的研究表明施入酸化糞污的土壤相對施入未酸化糞污的土壤其氨揮發損失降低了85%，提高了黑麥草對NH4+的利用率，同時也明顯提升了該土壤上種植黑麥草的干物質產量，同樣，也有研究[51]表明土壤表面施入酸化后的糞污能夠有效減少土壤N損失，促進作物對N的吸收。FANGUEIRO等[52]最新研究再次表明在燕麥播種0 和8 d后的土壤表面單獨施用酸化豬糞水或與尿素聯合使用均能有效降低NH3-N的排放，尿素和酸化豬糞水聯合應用還進一步提高了尿素的使用效率。

表3 糞污酸化貯存及施用肥效特征

3.4 對農田環境的影響

酸化后的糞水還田后可以提高土壤肥效，但不合理的酸化貯存技術及施用方式會降低糞水肥效，甚至引起二次污染[53-56]。主要原因是糞水中有大量以銨氮為主的鹽分，向糞水添加酸化劑會使銨鹽形態更加穩定，雖然降低了氨氣排放，但卻增加了糞水鹽分含量，鹽含量升高是糞水酸化還田的難點之一。

正如COCOLO等[57]研究表明，酸化后糞水固液分離出的干物質含量降低了10%～50%，這主要是由于糞污中部分固體物質在酸性條件下以無機鹽的形式溶出。HJORTH等[58]發現糞水中的無機沉淀物在酸性條件下溶解，使可溶性磷和可溶性鈣、鎂含量增加，糞水電導率增加。

另外，也有研究者發現不科學的酸化還田技術會帶來土壤酸化問題，如FANGUEIRO等[59]將糞污酸化至pH值為5.5短期存放后進行試驗，研究結果表明長期施用酸化后的糞污可能會導致土壤pH值降低。

HJORTH等[58]也發現類似現象，使用濃硫酸作為酸化劑會使土壤pH值降低。對于酸化糞水還田引起的鹽分過高問題，現有研究尚未提供系統解決方案[60-61]。而對于土壤酸化問題，部分學者研究提出延長糞水貯存時間等緩解路徑。如丁京濤等[62-64]發現隨著儲存時間的推移，還田前的糞污將呈中性乃至堿性，不足以對農田pH及其土壤肥效產生影響。因此科學的糞水酸化還田技術可有效減少糞水酸化對土壤的副作用。同時，結合中國農村環境和農田自然稟賦情況以及糞水酸化存儲技術特征，分析認為中國農村地區應采取養殖舍內長期酸化的酸化工藝，待酸化糞水存儲足夠長時間后還田利用。

4 結論與展望

糞水酸化貯存技術是一種成本低、操作簡單的糞水資源化利用技術，能夠有效減少糞水貯存及農田施用過程NH3的揮發損失，提高糞水肥效，同時糞水酸化貯存還田可有效減少養分流失，對促進中國種養循環、發展生態農業具有重要的意義。目前，歐美等發達國家對糞水酸化貯存及施用技術的研究較多，在國內仍處于初始探究階段，相關機理與技術研究存在許多不足。尤其是糞水酸化存儲過程中NH3和N2O排放規律尚不清楚，糞水酸化存儲過程NH3和溫室氣體產排微生物驅動機制和協同減排的系統研究相對缺乏，科學經濟的酸化技術工藝、應用標準研究依然不足。

因此，針對現有研究中存在的不足，未來應重點從以下幾方面深入研究：1）采用同位素示蹤等新型生化手段，結合定量PCR技術，探明糞水存儲過程中含氮氣體的產排規律，摸清糞水存儲過程中的氮素遷移轉化路徑；2）以復合酸化劑等作為研發重點，系統研究不同酸化劑、酸化方式對糞水的酸化效果，篩選出成本低、效果好的酸化劑，明確不同酸化劑、pH、貯存時間、貯存方式對糞水養分含量的影響效果及作用機制，進而確定科學合理的酸化技術工藝；3）研究酸化后糞水的農田施用效果及環境風險，分析酸化糞水施用后對土壤理化性質、土壤生物群落及酶活性、農作物生長及產量、養分淋溶損失、氨氣及溫室氣體排放等變化特性，制定糞水酸化還田技術標準，規范糞水還田方式與施用量，減少環境風險；4）在明確酸化機理及工藝參數的基礎上，開展適用于中小型養殖場的糞水酸化貯存裝備研發，同時要充分考慮相關酸化設備與設施的耐腐蝕性能，強化國內酸化貯存技術的推廣應用。

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Progress in the mechanism for the promotion of nitrogen loss reduction during the acidification storage of animal slurry

ZHANG Dongli, ZHANG Pengyue, SHEN Yujun, DING Jingtao※

(1.,,100125,; 2.,,100125,)

Acidification storage of animal slurry is one of the key technologies to effectively regulate the relationship between microorganisms, environment, and nitrogen for the high reduction of nitrogen loss and efficiency in animal slurry. This review aims to systematically investigate the nitrogen migration and transformation during the acidified storage of animal slurry in recent years. Three acidifiers were used, including the strong acid, hydrolyzed acidic salt, and easily decomposed organic matter. Three types of acidizing storage were then selected, namely long-term, medium, and long-term acidizing in the storage pool and short-term acidizing in the application. Finally, the economic cost and application effectiveness were comparatively evaluated in this case. More importantly, a systematic analysis was performed on the reduction of nitrogen losses and enhancement of fertilizer effectiveness, according to the technical route in the acidification storage. Furthermore, future research directions were addressed to identify the shortcomings of existing technologies for the acidified storage of animal slurry. Specifically, the nitrogen migration and transformation in the acidification storage process of animal slurry were divided into organic nitrogen mineralization, ammonium nitrogen fixation, inhibition of inorganic nitrogen conversion, and nitrification. Two reasons were attributed to reducing the nitrogen loss in the acidification storage of animal slurry. The addition of acidifiers was one way to change the dynamic balance of NH4+and NH3by lowering the pH of animal slurry, in order to promote the formation of NH4+while reducing the emission of dissolved NH3in animal slurry. The microbial activity decreased with the decreasing pH and mineralization of organic matter in animal slurry, thus reducing the production and emission of NH3. The acidification storage of animal slurry reduced the NH3emissions by 15%-77%. The degradation rate of nitrogenous organic compounds decreased with the addition of acidifiers, leading to the lower production of ammonium nitrogen. And the conversion rate of ammonium nitrogen to nitrate nitrogen was also reduced, thus further reducing the conversion of nitrate nitrogen to N2O. To sum up, the nitrogen losses were reduced to alter the microbial action and chemical equilibrium state. In addition, the long-term acidizing process presented more stable acidizing and a wider application range during the application, compared with the medium and long-term acidizing in the storage pool and the short-term acidizing. The acidification storage of animal slurry can be expected to stabilize and retain NH4+in the animal slurry. Therefore, acidification and returning to the field can improve the content of effective nutrients (such as N and P) in the soil for the high efficiency of soil fertility. However, the low efficiency of manure fertility and the secondary pollution can also be found in the unreasonable acidification storage and application in practice. It is a high demand for the quantitative analysis of nitrogen migration and transformation pathways in the process of fecal water storage, the complex acidifiers, and the post-acidification animal slurry in agricultural fields. The assessment and response to environmental risks can be launched for the research and development of acidification storage equipment in the future.

acids; fertilizer efficiency; animal slurry; nitrogen loss reduction

2022-11-05

2022-03-30

農業農村部規劃設計研究院自主研發項目：廢棄物肥料化利用創新團隊（CXTD-2021-11）；青年拔尖人才支持計劃（SQ2022QB00354）；典型畜禽養殖場不同類型糞水資源價值與安全性綜合評估技術（21327304D）

張冬麗，博士，工程師，研究方向為農業廢棄物資源化利用技術研發。Email：dongliustb@126.com

丁京濤，高級工程師，研究方向為農業廢棄物資源化利用與環境保護技術研發。Email：dingjingtao@163.com

10.11975/j.issn.1002-6819.202211070

S21；X713

A

1002-6819(2023)-08-0012-08

張冬麗，張朋月，沈玉君，等. 畜禽養殖糞水酸化貯存及氮素減損增效研究進展[J]. 農業工程學報，2023，39(8)：12-19. doi：10.11975/j.issn.1002-6819.202211070 http://www.tcsae.org

ZHANG Dongli, ZHANG Pengyue, SHEN Yujun, et al. Progress in the mechanism for the promotion of nitrogen loss reduction during the acidification storage of animal slurry[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2023, 39(8): 12-19. (in Chinese with English abstract) doi：10.11975/j.issn.1002-6819.202211070 http://www.tcsae.org