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Demand Characteristics of Alkalinity for Anaerobic Sequencing Batch Reactor

机译：厌氧顺序分批反应器的碱度需求特征

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A considerable amounts of alkalinity added into the anaerobic reactor is a major cost , and related directly to the economic feasibility in the anaerobic treatment processes for high-strength carbohydrate wastewater. In order to minimize this cost, the anaerobic reactor is expected to operate stably under lower pH and lower alkalinity. The objectives of this paper were to investigate the demand characteristics of alkalinity for anaerobic sequencing batch reactor (ASBR) to treat high-strength carbohydrate wastewater, as well as the determination of the minimum alkalinity and pH compatible with stable long-term operation. The experiment was carried out in a lab-scale ASBR reactor of 6L effective capacity, with granulated anaerobic sludge of 1-2mm diameter. Instantaneous inflow was used in whole experiment. Using glucose as substrate, the substrate concentration was adjusted at a COD value of 6700 mg/L by addition of tap water. The organic loading rate(OLR) was 10.0gCOD/(g·d), with COD removal efficiencies being higher than 90%. Sodium bicarbonate was added into the influent to control and adjust pH and alkalinity of digesting liquid, and alkalinity levels were characterized by the ratio of COD to alkalinity of the influent, (I.e. COD/Alk).The Dosages of the alkalinity added into the influent were decreased step by step in the experiment. Different ratios of COD/Alk, 1.0:1, 2.0:1, 2.5:1, 3.4:1, 4.2:1 and 4.8:1, were respectively studied. After more than 2 years of operation, a successful anaerobic treatment operation under lower pH and lower alkalinity was achieved. The results showed significant effects of alkalinity levels on volatile fatty acids(VFA) accumulated concentrations, especially acid-production rate within the first 0.5h of reaction periods. The maximum concentration of VFA accumulated in the digesting liquid increased to 1626mg/L, at the same time the minimum pH value decreased to 6.10 at the COD/Alk ratios of 4.2:1 and 4.8:1, which indicated that the digestion liquid in the reactor was acidic. Alkalinity levels had influences on CO2%, bicarbonate alkalinity (Balk) and pH too. The variation of CO2 partial pressure was between 44% and 55% at the 2.0:1 alkalinity level, but the variation was between 41% and 55% at the ratio of 4.8:1.The minimum Balk in the reactor was merely 423mg/L when the ratio of COD/Alk was 4.8:1, and the ratio of Balk to (total alkalinity )Talk was 0.4 correspondingly, simultaneously, the pH values in whole reaction period were almost always below 6.5, which was less than the lowest limit value recommended for the continuous-flow anaerobic processes. During operation of all alkalinity levels, the behavior of process was steady with COD removal efficiency higher than 97% and COD concentration of effluents lower than 198mg/L, and no signs of instability. The results proved feasibility at the lowest alkalinity for ASBR because of its intrinsic characteristics. The minimum alkalinity demand dose expressed by the ratio of COD/Alk was 4.8:1(0.21gCaCO3/gCOD).
机译：添加到厌氧反应器中的大量碱度是主要成本，并且直接涉及高强度碳水化合物废水的厌氧处理过程中的经济可行性。为了最小化该成本，期望厌氧反应器在较低的pH和较低的碱度下稳定运行。本文的目的是研究厌氧测序间歇式反应器（ASBR）处理高强度碳水化合物废水的碱度需求特征，以及确定最低碱度和pH值以及稳定的长期运行。实验是在实验室规模的6升有效容量的ASBR反应器中进行的，该反应器的颗粒厌氧污泥直径为1-2mm。在整个实验中使用瞬时流入。使用葡萄糖作为底物，通过添加自来水将底物浓度调节为6700 mg / L的COD值。有机负荷率（OLR）为10.0gCOD /（g·d），COD去除率高于90％。向进水中加入碳酸氢钠以控制和调节消化液的pH值和碱度，碱度水平通过COD与进水碱度之比（即COD / Alk）来表征。在实验中逐步减少。研究了COD / Alk的不同比例，分别为1.0：1、2.0：1、2.5：1、3.4：1、4.2：1和4.8：1。经过两年多的运行，在较低的pH和较低的碱度下成功完成了厌氧处理操作。结果表明，碱度对挥发性脂肪酸（VFA）的累积浓度有显着影响，特别是在反应周期的前0.5h内产酸速率。在4.2：1和4.8：1的COD / Alk比下，消化液中积累的VFA的最大浓度增加到1626mg / L，同时最小pH值降低到6.10。反应器是酸性的。碱度也影响CO2％，碳酸氢盐碱度（Balk）和pH。在碱度为2.0：1的条件下，CO2分压的变化在44％至55％之间，而在4.8：1的比例下，CO2分压的变化在41％至55％之间。反应器中的最小Balk仅为423mg / L当COD / Alk比为4.8：1，Balk与（总碱度）Talk的比值分别为0.4时，同时，整个反应期间的pH值几乎总是低于6.5，低于最低限值推荐用于连续流厌氧工艺。在所有碱度水平下运行过程中，工艺行为稳定，COD去除效率高于97％，废水的COD浓度低于198mg / L，并且没有不稳定的迹象。由于其固有的特性，结果证明了在最低碱度下ASBR的可行性。用COD / Alk之比表示的最低碱度需求剂量为4.8：1（0.21gCaCO3 / gCOD）。

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