豬糞尿水初次消化液與稻稈、竹材之厭氧共消化

Abstract

隨著台灣的養豬戶慢慢轉向大規模養殖，為滿足所需的廢水排放標準，針對養豬場廢水處理系統的需求將越來越高。台灣常見的廢水處理方式是由畜產試驗所（Taiwan Livestock Research Institute, TLRI）開發的三段式處理系統，其中包括1）固液分離、2）厭氧消化以及3）好氧處理，依次進行。然而，由於好氧處理的耗能性質，因此提出了另一種省略好氧池的處理系統：可用第二階段厭氧反應槽代替好氧池，第一階段厭氧反應槽的污水可與農業廢棄物如稻草（RS）和林業廢棄物如竹子廢棄物（BW）共同消化。第二階段厭氧共消化代替好氧池的優點是，除了可處理更多的廢棄物，同時又可減少厭氧池的能量消耗，又可產生更多的再生能源。 在本研究，豬糞尿初次消化液（Swine Wastewater Effluent, SWE）是由實驗室規模的第一階段連續攪拌式反應槽 （Continuously Stirred Tank Reactor, CSTR）中所收集，該CSTR在37oC和HRT 10天內消化了TS為8%的新鮮豬糞尿（Fresh Swine Manure, FSM）。第二階段的厭氧CSTR在37oC下分批進行。SWE的量固定為3,000 mL，RS+BW的量固定為200 g。本研究的目的是比較不同的RS：BW混合比例對厭氧共消化之差異，共進行了 100：0（R100）、80：20（R80）、60：40（R60）、40：60（R40）、20：80（R20）和0：100（R0）6個批次的試驗。每一批次都是兩重複（Duplicate），包括參考點的空白試驗。 由於RS具有較佳的生物降解性，因此RS比率越高，固體去除率越高，單位VS的甲烷產量就越高。實驗結果顯示最低和最高的總固形物去除率（s-RTS）分別為R0批次的8.09%和R100批次的49.84%。最低和最高的揮發性固形物去除率（s-RVS）在批次R0和批次R100中分別為12.17%和57.37%。單位甲烷產量（Methane Yield）在R0中最低，為0.036 L CH4/g VS added，R80中最高，為0.171 L CH4/g VS added，而R100的單位甲烷產量僅略低於R80為0.169 L CH4/g VS added。就去除的VS而言，所有批次的單位甲烷產量平均為0.311 L CH4/g VS destroyed，它也可以被視為VS-甲烷轉化率。至於BW的生物降解性比RS低的原因，過去的研究曾指出纖維素和木質素之和與厭氧生物降解性呈負相關，而本研究所呈現的結果與前人的研究一致。

As Taiwan’s swine farmers are moving away from small scale farming to bigger scale farming, more swine farms will need proper wastewater management to meet the required wastewater discharge standard. The common state-of-the-art wastewater treatment in Taiwan is three-stage treatment system developed by Taiwan Livestock Research Institute (TLRI), which includes 1) solid-liquid separation, 2) anaerobic digestion, and 3) aerobic treatment, in sequence. However, since the aerobic treatment is energy intensive, another alternative treatment system without one is proposed: the aerobic tank could be substituted with second-stage anaerobic reactor which co-digest effluent from first-stage anaerobic reactor as the seeding bacteria with agricultural waste, such as rice straw (RS), and forestry waste, such as bamboo waste (BW). The advantage of second-stage anaerobic co-digestion instead of aerobic treatment is that it can treat additional waste, which otherwise would go untreated, while at the same time produce more green bio-energy and save cost. This research explored this idea by experimenting with anaerobic co-digestion in the second-stage anaerobic reactor, using first-stage anaerobic effluent as the seeding bacteria. In this research, swine wastewater effluent (SWE) was collected from simulated, lab scale, first-stage semi-continuous anaerobic CSTRs that digested TS 8% of fresh swine manure (FSM) at 37 ± 1 oC and HRT 10 days. The second-stage anaerobic CSTRs were operated in batch at 37 ± 1 oC. The amount of SWE was fixed with 3000 mL : 200 g ratio compared to biomass mixture, which comprises of RS and BW. The aim of this research is to investigate the differences among 6 different RS:BW mixing ratios: 100:0 (R100), 80:20 (R80), 60:40 (R60), 40:60 (R40), 20:80 (R20), and 0:100 (R0). Each was done in duplicate, including blanks for the reference point. Since RS has better biodegradability, the higher the RS ratio, the higher the solids removal efficiency, and the higher the methane yield per gram of VS added. Lowest and highest s-RTS is 8.09% in batch R0 and 49.84% in batch R100, respectively. Lowest and highest s-RVS is 12.17% in batch R0 and 57.37% in batch R100, respectively. The methane yield is lowest in R0 at 0.036 L/g VS added, and the highest in R80 at 0.171 L/g VS added, although R100 methane yield was only slightly below at 0.169 L/g VS added. In terms of VS destroyed, all of the batches averaged at methane yield of 0.311 L/g VS destroyed. It could also be interpreted as VS-methane conversion rate. As for the reason of lower biodegradability in BW as compared to RS, lignocellulosic composition analysis of them was done. Three other studies were also incorporated in the lignocellulosic composition comparison. The result was in line with previous studies’ conclusions that the lignin content is negatively correlated with anaerobic biodegradability. Thus, higher lignin content would yield lower biogas and methane yield.