Q&A about UASB

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The key aspect of a three-phase separator lies in that area; please give some guidance on how to design it. Answer: The question itself is the key point, and different people have varying opinions on what constitutes the key element, which is why there are various types of three-phase separators. I have a few personal insights to share with everyone: (1) What is the function of a three-phase separator? A: It is to retain a sufficient amount of active sludge inside the UASB ； B: Screen the sludge. When designing, focus firmly on the main functions while also taking into account the auxiliary functions. (2) When designing a UASB, it is necessary to estimate (determine in advance) the particle size and specific gravity of the sludge (whether the sludge will be in granular form in the future), as well as the size of the bubbles produced by the sludge. (3) Understand the principle of “sludge loss” in UASB. I believe that the reasons for loss are varied, but under normal operating conditions (not during periods of acidification, without acute poisoning, without hydraulic or load shocks, …), the loss is gradual, and catastrophic outcomes result from the accumulation of long-term problems. Sludge loss is caused by the bubbles attached to the sludge; when the \"cluster\" formed by the sludge and these bubbles moves at the same speed as the water flow, it gets carried away. (4) The importance of \"theoretical calculations\" is far less than that of engineering experience and lessons learned; and understanding these lessons relies on \"theory\" – otherwise, blind \"improvements\" will yield only half the results with twice the effort. (5) In addition to process-related issues, engineering problems such as mechanics, materials, corrosion prevention, etc., should also be addressed; often, small problems can lead to major issues, just as a long dike can be destroyed by ant holes. (6) Cost is also a major issue; prices in the past were not normal, and now competitiveness through better design and other technologies is necessary. Question: What is the proportion of domestic UASB units that reach their designed load? I’ve heard that in China, the proportion of equipment capable of producing true granular sludge using UASB is less than 50% – is that correct? Answer: The day before yesterday, a Ph.D. student from Tsinghua University was talking with my friend about the current situation of UASB, and he said: It’s not good at all! Last month, someone in our “club” also pointed out this issue. Be polite and ask about the situation regarding reaching the design load In other words, it is the designer who rates themselves. We in our small unit don’t know much about the overall situation in the country. But indeed, a lot has been seen and heard, and everyone is not optimistic. In my opinion, the reasons are: (1) People have overly high expectations for UASB ； (2) Making too many promises to the owner, resulting in overly high expectations on their part ； (3) Designers read a lot and conduct few experiments; the experimental time is not long enough, so they dare to use any kind of water ； (4) The designed load is too high; it does not take into account unfavorable factors such as fluctuations in industrial production, low operational levels, and poor quality of equipment, etc ； (5) Some environmental protection equipment manufacturers are acting recklessly, focusing only on securing projects without caring about delivering high-quality work ； (6) The stability of UASB is problematic in itself; my colleagues at the research institute say that UASB is like a weight loss drug – anyone who uses it loses weight. So, we are now using MIC. MIC has better stability than UASB. (7) If there are problems with the UASB, it costs money to replenish the microorganisms ； It takes time—to re-debug. Question: What is the main core of three-phase separator design? How is its angle determined based on water quality and process parameters? How to prevent mud from appearing in the water outlet and how to overcome the foam problem? Answer: The key (core) of the three-phase separator is to ensure that the amount of sludge generated is greater than the amount lost, so that the amount of sludge in the reactor increases. Anything that can achieve this goal is a \"good\" three-phase separator; don’t be constrained by form, and don’t fall into the shackles of those who came before. So, I say too much and it increases the risk in this regard; it’s better not to say anything. It’s impossible to prevent mud from coming out with the water; there’s no need to try. Question: How to cultivate granular sludge? It is said that in domestic UASBs, it is extremely difficult to cultivate granular sludge with high treatment efficiency. Answer: Once the type of wastewater and the reactor structure are determined, granular sludge is not cultivated; it is a result, a product of design and operation. Do you mean that there is no granular sludge in domestic UASBs? ! I basically agree, but not all domestic UASBs lack granular sludge; I know that some UASBs maintain good granular sludge over a long period of time. The relationship between granular sludge and treatment efficiency may not be as you think. The removal efficiency of anaerobic pollutants is more closely related to factors such as the type of wastewater and the retention time, rather than whether granular sludge is present. So, “granular sludge with relatively high treatment efficiency.” ”There may be two objectives here: one is processing efficiency, and the other is granular sludge.