We all know that activated sludge is a "great hero" in sewage treatment, just like diligent little guards who diligently decompose pollutants in sewage. But if they encounter some 'tough character' wastewater, this little guard will also suffer. Today, let's talk about the toxic wastewater from activated sludge, their impact on activated sludge, and how we should respond.
Heavy metal wastewater: the deadly poison of activated sludge
Wastewater containing heavy metals such as mercury, cadmium, lead, and chromium is a deadly poison for activated sludge. Heavy metal ions will tightly adhere to the cell surface of microorganisms in activated sludge and then penetrate into the interior of the cells. This can be a bad thing once it goes in, as it will "fight" with some key enzymes in the cell, making these enzymes unable to function properly. Enzymes are the "powerful assistants" for microorganisms to carry out various life activities. If enzymes are inactivated, microorganisms cannot decompose organic matter in sewage normally, and the activity of activated sludge decreases sharply. For example, activated sludge is originally full of vitality, like an tireless athlete, and can efficiently treat sewage. But once encountering heavy metal wastewater, it is like an athlete being injected with an anesthetic, unable to exert energy all over their body, and the efficiency of treating sewage may drop from 80% to 20% or even lower, resulting in serious water quality exceeding the standard.
In the face of heavy metal wastewater, the first step is to control it at the source. The factory needs to improve its production process and minimize or eliminate the use of raw materials containing heavy metals. If heavy metal wastewater has already been generated, it needs to be pretreated first. Chemical precipitation method can be used to add chemicals to allow heavy metal ions to precipitate and separate from water, reducing the concentration of heavy metals to a range that activated sludge can withstand, and then discharging them into the sewage treatment system.
Cyanide containing wastewater: a 'killer' that destroys microbial respiration
Cyanide containing wastewater is also a major enemy of activated sludge. Cyanide has significant toxicity to microorganisms, mainly disrupting their respiration. Microorganisms obtain energy through respiration, just like humans need to breathe to survive. Cyanide can block the electron transfer in the microbial respiratory chain, preventing microorganisms from producing energy normally. Without energy, microorganisms cannot carry out important activities such as absorbing nutrients and decomposing organic matter. The activated sludge, which was originally vibrant and rich in microbial communities, has experienced a sharp decrease in microbial numbers and a monotonous microbial community structure under the impact of cyanide containing wastewater. The originally complex and diverse ecosystem is like a prosperous small town suddenly facing a disaster, with residents fleeing one after another, leaving only a few survivors.
The common treatment method for cyanide containing wastewater is to use cyanide breaking technology. For example, the alkaline chlorination method involves adding chlorine based oxidants to wastewater under alkaline conditions to oxidize cyanide into harmless nitrogen and carbon dioxide. Firstly, the highly toxic cyanide is converted into slightly less toxic cyanate through primary oxidation, and then further oxidized to completely eliminate toxicity, ensuring that the wastewater entering the activated sludge treatment system is safe and harmless.
High concentration organic wastewater: a sweet burden
What we are talking about here is not ordinary organic wastewater, but the kind with particularly high concentration, such as wastewater generated in the food processing and brewing industries. The organic content of this type of wastewater is extremely high, and the chemical oxygen demand (COD) can easily reach thousands or even tens of thousands. High concentration organic wastewater is like a super rich and exaggerated feast presented in front of activated sludge. At first, the microorganisms were very happy and crazily "ate" to decompose organic matter. But this' feast 'is too much and too fierce, and microorganisms cannot digest it. A large amount of organic matter will consume dissolved oxygen in water, causing rapid oxygen depletion in the water. Aerobic microorganisms in activated sludge lose oxygen, just like fish without water, unable to survive and work normally. Moreover, in the absence of oxygen, some metabolic products such as organic acids are also produced, which lowers the pH value of the wastewater and further inhibits the growth of microorganisms. The activated sludge system, which originally had a stable treatment effect, has a serious decrease in treatment capacity under the impact of high concentration organic wastewater, and the COD of the effluent will also increase significantly.
To deal with high concentration organic wastewater, anaerobic aerobic combined treatment process is usually adopted. First, let the wastewater enter the anaerobic reactor. In an anaerobic environment, anaerobic microorganisms decompose large organic molecules into small molecules, reducing the COD concentration of the wastewater. At the same time, they can also produce biogas, achieving energy recovery. After anaerobic treatment, the wastewater enters the aerobic treatment stage, and the aerobic microorganisms in the activated sludge are used to further decompose the remaining organic matter, which can effectively reduce the treatment burden of activated sludge and ensure the treatment effect.
Strong acid and strong alkali wastewater: the "bully" who changes the environment
The impact of strong acid and alkali wastewater with low or high pH values on activated sludge should not be underestimated. Microbial growth requires a suitable pH environment, typically between 6.5-8.5. After strong acid wastewater (pH value far below 6.5) or strong alkali wastewater (pH value far above 8.5) enters the activated sludge system, it is like a bully breaking into the originally harmonious town, causing a mess in the environment. Acidic environment can cause protein denaturation on the surface of microbial cells, affecting their absorption of nutrients; Alkaline environment may disrupt enzyme activity and metabolic pathways within microbial cells. Under the influence of strong acid and alkali wastewater, a large number of microorganisms in activated sludge will die, and the settling performance of activated sludge will also deteriorate, resulting in problems such as sludge flotation, and the entire sewage treatment system will fall into chaos.
The key to solving the problem of strong acid and strong alkali wastewater is to adjust the pH value. Set up an acid-base neutralization tank before the wastewater enters the activated sludge treatment system. If it is acidic wastewater, add alkaline substances such as lime and sodium hydroxide for neutralization; If the wastewater is alkaline, acidic substances such as sulfuric acid and hydrochloric acid should be added to adjust the pH value of the wastewater to a range suitable for microbial growth, and then further treatment should be carried out.
