摘要
糖蜜酒精废液是制糖工业中最重要的污染源。传统糖蜜酒精发酵工艺是将酒精成熟醪直接送入蒸馏塔,蒸馏废液中因含有大量的酵母残体,而造成COD、BOD含量高,直接排放不但对水体、土壤等环境造成严重污染,甚至会危害到人类的健康。
本文针对这一问题对传统工艺加以改进：采用膜分离技术对甜菜糖蜜酒精成熟醪进行处理,分离后的酒精酵母回用发酵。这样不但可以减小废液的污染程度,还可以节约酒精酵母资源,为糖蜜废液酒精的资源化治理提供了新思路。本文的主要研究内容与结果如下：
首先,本文采用微滤对酒精成熟醪进行处理,分离得到含酵母菌体的浓缩液,循环回用于发酵,透过液送至蒸馏。对微滤前后的蒸馏废液进行比较,得到以下结论：未经处理的成熟醪直接蒸馏,得到的废液COD值高达139302.727 mg·L-1,经微滤处理后的成熟醪蒸馏废液COD值降为74288.217 mg·L-1,比较得出微滤前后COD去除率达到46.67%,乙醇损失为3.46%,可以有效的减小废液的治理难度,比离心处理的效果好,能耗较离心低,易于工业化,易于密闭条件操作,减少乙醇损失,且不易染菌。
其次,本文对微滤的条件进行了初步的优化,分别使用0.01μm,0.02gm孔径的微滤膜,对膜孔径和操作压力两个影响因素进行了研究：根据料液处理量不同,选择不同操作条件,微滤效果更佳。相同膜孔径的条件下,操作压力越大,初始膜通量越大,但是膜通量随时间的下降速度也越快,在处理少量醪液时,可以选择选用较高的操作压力(安全压力之内),反之,选择低操作压力微滤速度相对更快,更稳定；在相同操作压力条件下,比较不同膜孔径的膜通量,膜孔径越大,初始膜通量越大,但是随时间的下降速度也越快,且膜内压力上升较快,适合少量料液的处理；反之,在长时间处理大量料液时,小孔径的微滤膜速度相对更快。同时本文考察了不同操作压力下的微滤效果,综合考虑乙醇损失率与COD去除率,选择0.01μm,0.04Mpa操作压力为优化条件。
最后,本文对酒精酵母回用发酵的发酵特性进行了研究比较,并对甜菜糖蜜发酵条件进行了初步的优化：初始糖浓度在26°Bx,接种量为8%,初始pH为4.2,30℃,140rpm条件下发酵36h,为最优发酵条件；本文将微滤分离出的酵母循环回用,连续循环5批后,比较发酵特性参数,酵母得率与酸化力呈下降趋势,然而糖醇转化率与糖转化率变化不明显,基本保持稳定,循环回用过程乙醇得率可以提高约1%,发酵周期缩短了6-12h,说明该工艺可行,既可以节省酵母资源,又可以缩短发酵周期,提高设备的利用率,提高产率。
Molasses alcohol wastewater is the most important source of pollution in sugar-making industry. Traditional process of fermentation is to directly transfer the fermented mash into distillation tower. However, COD and BOD of wastewater are both of a high level, because of the large amount of yeast residue. Its direct discharge seriously pollutes water, soil, and the human health as well.
In this paper, the traditional process was improved:the separation and reuse of the yeast in the mature mash by applying the microfiltration technology have been studied. This new disposal method not only can reduce the pollution of waste water, but also save the resources of alcohol yeast. It can provide new pathway for industrialization treatment of molasses alcohol waster water. The main contents of experiment were as follow:
First, the concentrated liquid was isolated from the mature mash by microfiltration, loops back for a new fermentation, and supernatant mash was transferred to distill. Comparing the wastewater before and after microfiltration, the following conclusions were drawn:COD of untreated mash which was directly distilled is up to 139302.727 mg·L-1, while that of the wastewater coming from the treated mature mash reduced to 74288.217 mg·L-1, the removal rate of COD is 46.67%, and the loss of ethanol is 3.46%. It's better than the effect of centrifugal treatment, lower than centrifugal energy consumption, and more suitable for industrialization than centrifugation. Apart from its effective reduction of the difficulty in waste treatment, it can operate in confined conditions Where is easy to control the loss of ethanol and can hardly be contaminated by other bacterial.
Secondly, the conditions of the microfiltration were optimized. Two factors, pore size of membrane and the operating pressure, were studied respectively: effect of microfiltration is better when different operating conditions were chosen corresponding to different liquid handling capacity. In condition of the same pore size, a greater operating pressure brought a larger initial flux through the membrane. Otherwise the decline in membrane flux was faster, while membrane flux rate of decline over time is faster, and the operating pressure increased fast, which is more suitable for a small amount of mash treatment; In condition of the same operating pressure, a greater pore size brought a larger initial flux through the membrane, otherwise the decline in membrane flux was faster, and the great pore size membrane is more suitable for a small amount of mash treatment, on the other hand, in case of a large amount of liquid for a long processing time, a small pore size is relatively more effective. This paper Studied additionally on the microfiltration effect under different operating pressure, by considering the loss rate of ethanol and the COD removal efficiency, it's concluded that a 0.01μm pore size membrane and 0.04Mpa operating pressure is the optimized condition.
Finally, the reuse of alcohol yeast was studied and beet molasses fermentation conditions were optimized:the optimal fermentation conditions could be initial sugar concentration of 26°Bx, inoculum of 8 %, pH 4.2,30℃,140 rpm fermented for 36 h; After five consecutive cycles fermentation, the yeast yield rate and the acidification decreased, while the ethanol yield increased almost 1%, shortened the fermentation period about 6-12h, and sugar alcohols and sugar conversion rate did not change significantly and remaine stable, indicating that the technology is feasible, which can economize yeast resources, improve the utilization of equipment rate, shorten the fermentation cycle, and improve the ethanol yield.
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