一般来说，对于以产甲烷为主要目的的厌氧过程要求pH值在6.5~8.0之间，废水碱度偏低或运行负荷过高时，会引起反应器内挥发酸积累，导致产甲烷菌活力丧失而产酸菌大量繁殖，持续过久时，会导致产甲烷菌活力丧失殆尽而产乙酸菌大量繁殖，引起反应器系统的“酸化”。严重酸化发生后，反应器难以恢复至原有状态。
Generally speaking, for the anaerobic process with the main purpose of methanogenesis, the pH value is required to be between 6.5 and 8.0. When the wastewater alkalinity is low or the operation load is too high, it will cause the accumulation of volatile acid in the reactor, resulting in the loss of methanogenic bacteria activity and the proliferation of acidogenic bacteria. If it continues for too long, it will cause the loss of methanogenic bacteria activity and the proliferation of acetic acid producing bacteria, causing the degradation of the reactor system“ Acidification ". After serious acidification, it is difficult for the reactor to return to its original state.
“酸化”：①沼气产量下降;②沼气中甲烷含量降低;③消化液VFA增高;④有机物去除率下降;⑤消化液pH值下降;⑥碳酸盐碱度与总碱度之间的差值明显增加;⑦洗出的颗粒污泥颜色变浅没有光泽;⑧反应器出水产生明显异味;⑨ORP(氧化还原电位)值上升等。
"Acidification": ① decrease of biogas production; ② decrease of methane content in biogas; ③ increase of VFA in digested liquid; ④ decrease of organic matter removal rate; ⑤ decrease of pH value of digested liquid; ⑥ obvious increase of difference between carbonate alkalinity and total alkalinity; ⑦ lightening and tarnishing of washed granular sludge; Ⅷ obvious peculiar smell in reactor effluent; Ⅸ increase of ORP value, etc.
厌氧反应器酸化的原因
Causes of acidification in anaerobic reactor
1、厌氧反应器超负荷运行
1. Overload operation of anaerobic reactor
我们都知道，在运行厌氧反应器的各项工艺控制条件中，污泥负荷是一个非常重要的控制参数。污泥负荷是指单位时间内施加给单位质量厌氧污泥的有机物的量，以kgSCOD/kgVS.d表示。对于某种废水，厌氧污泥具有一个限制值，当运行的负荷超过该限制值，则意味着超负荷运行。
As we all know, sludge load is a very important control parameter in various process control conditions of anaerobic reactor. Sludge load refers to the amount of organic matter applied to anaerobic sludge per unit mass in unit time, expressed in kgscod / kgvs. D. For a certain wastewater, anaerobic sludge has a limit value. When the operating load exceeds the limit value, it means overload operation.
虽然该限制值从污泥负荷的概念上理解是针对整个厌氧污泥，实际上真正的对象是针对厌氧污泥中的产甲烷菌。超负荷运行，实际上就是负荷量超过了厌氧污泥中产甲烷菌的产甲烷能力，而此时的负荷量往往并没有超过厌氧污泥的水解酸化能力。所以就出现了反应器的VFA开始累积，浓度不断上升，出水pH值降低，去除效率下降这种污泥酸化现象的发生。
Although the limit value from the concept of sludge load is for the whole anaerobic sludge, in fact, the real object is for methanogens in anaerobic sludge. In fact, overload operation means that the load exceeds the methanogenic capacity of methanogens in anaerobic sludge, while the load does not exceed the hydrolytic acidification capacity of anaerobic sludge. So the VFA of the reactor began to accumulate, the concentration increased, the pH value of the effluent decreased, and the removal efficiency decreased.
所以，了解厌氧反应器的污泥总量，并以此来维持合理的运行负荷，是预防厌氧反应器出现酸化的重要手段之一。
Therefore, understanding the total amount of sludge in anaerobic reactor and maintaining reasonable operation load is one of the important means to prevent acidification in anaerobic reactor.
2、pH值、温度等运行控制条件出现严重偏差
2. Serious deviation occurred in pH value, temperature and other operation control conditions
由于厌氧污泥中产甲烷菌对其生存条件的要求比水解酸化菌苛刻的多，所以当反应器的pH值或温度的控制范围出现很大的偏差，就会使产甲烷菌的产甲烷能力受到严重影响，而水解酸化菌所受到的影响却远远小于产甲烷菌，其结果同样会导致厌氧反应器发生酸化现象。
Because the requirements of anaerobic sludge methanogens on their living conditions are much more stringent than those of hydrolytic acidification bacteria, when the pH value or temperature control range of the reactor deviates greatly, the methanogenic ability of methanogens will be seriously affected, while the influence of hydrolytic acidification bacteria is far less than that of methanogens, which will also lead to the acidification of anaerobic reactor Elephant.
3、毒性物质流入
3. Inflow of toxic substances
厌氧污泥相比与好氧活性污泥，更容易受到毒性物质的抑制。和上述两点所阐明的一样，事实上更容易受到毒性物质抑制的也是厌氧污泥中的产甲烷菌而非水解酸化菌。当废水中含有某种或多种毒性物质，其浓度还不足以严重抑制厌氧污泥中的水解酸化菌时，产甲烷菌就已经受到抑制，污泥酸化现象就随之发生。
Compared with aerobic activated sludge, anaerobic sludge is more easily inhibited by toxic substances. In fact, methanogens in anaerobic sludge are more susceptible to toxic substances than hydrolytic Acidifiers. When the wastewater contains some or more toxic substances, the concentration of which is not enough to seriously inhibit the hydrolysis acidification bacteria in anaerobic sludge, the methanogens have been inhibited, and the sludge acidification phenomenon will occur.
因此，应对污染源可能存在的毒性抑制物进行排查，并建立污染物排放源和污水站之间的事故排放通报机制，和潜在的毒性物质日常监测机制，是防止此类厌氧反应器酸化事故的有效应对措施。
Therefore, it is an effective measure to investigate the toxic inhibitors that may exist in the pollution source, establish the accident discharge notification mechanism between the pollutant discharge source and the sewage station, and establish the daily monitoring mechanism of potential toxic substances.
4、营养盐投加严重不足
4. There is a serious shortage of nutrients
对于某些缺乏诸如N、P或其他微量元素的废水，投加足量的营养盐非常必要。因为厌氧污泥中无论是产甲烷菌还是水解酸化菌，都需要这些元素进行新陈代谢以及合成细胞物质。
It is necessary to add enough nutrients to some waste water which lacks n, P or other trace elements. Both methanogens and hydrolytic Acidifiers need these elements to metabolize and synthesize cell substances in anaerobic sludge.
当废水中的某种或多种营养元素缺乏时，将会严重影响产甲烷菌的活性。这是因为，对厌氧污泥，尤其是厌氧颗粒污泥来说，产甲烷菌位于颗粒污泥的部位，水解酸化菌则包裹在产甲烷菌的外围，水解酸化菌较产甲烷菌更容易获得这些元素来进行新陈代谢，再加之水解酸化菌的生殖速率又远远高于产甲烷菌，使得废水中原本不足的营养元素被水解酸化菌利用殆尽，而产甲烷菌得不到这些必要的元素进行生命活动，其活性会受到很大的抑制。其结果是，反应器的酸化不可避免。
The activity of methanogens will be seriously affected when one or more nutrients are deficient in wastewater. This is because for anaerobic sludge, especially for anaerobic granular sludge, methanogens are located in the center of granular sludge, while hydrolytic acidification bacteria are wrapped around methanogens. Hydrolytic acidification bacteria are more likely to obtain these elements for metabolism than methanogens. In addition, the reproductive rate of hydrolytic acidification bacteria is much higher than methanogens, which makes the waste water insufficient The nutrient elements are used up by hydrolytic acidification bacteria, but the activity of methanogens will be greatly inhibited if they can not get these essential elements for life activities. As a result, acidification of the reactor is inevitable.
酸化”恢复措施
Recovery measures of acidification
1、降低负荷
1. Reduce the load
反应器发生“酸化”的主要原因是产甲烷菌被抑制，而厌氧反应器的容积负荷是由污泥负荷决定的，甲烷菌活性降低，直接反映了污泥负荷的下降。所以在发生“酸化”时应及时控制进水，情况严重时应完全停止进水。
The main reason of "acidification" is the inhibition of methanogens. The volume load of anaerobic reactor is determined by the sludge load. The decrease of methanogens activity directly reflects the decrease of sludge load. Therefore, the influent should be controlled in time when acidification occurs, and the influent should be stopped completely when the situation is serious.
2、投加碱度
2. Adding alkalinity
厌氧反应器“酸化”时，可以向反应器中投加碱度中和过高的VFA来维持pH值的稳定，保证产甲烷菌的生存环境，防止严重“酸化”。NaHCO3、Na2CO3、NaOH、Ca(OH)2等都是常用来调节碱度的化学药剂，虽然投加NaOH或者Ca(OH)2等强碱性物质能够快速提高反应器内的pH值，但是氢氧化物会消耗产甲烷过程中所需的CO2，破坏产甲烷的进行，对产甲烷菌的恢复不利，因此不宜采用NaOH和Ca(OH)2。
When the anaerobic reactor is acidified, VFA with high alkalinity neutralization can be added to the reactor to maintain the stability of pH value, ensure the living environment of methanogens and prevent serious acidification. NaHCO3, Na2CO3, NaOH, Ca (OH) 2 are commonly used to adjust the alkalinity of the chemical agents. Although the addition of NaOH or Ca (OH) 2 and other strong alkaline substances can quickly improve the pH value in the reactor, but the hydroxide will consume the CO2 required in the process of methanogenesis, destroy the process of methanogenesis, and is not conducive to the recovery of methanogenic bacteria, so NaOH and Ca (OH) 2 should not be used.
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