How to solve the problem of excessively high key indicators in wastewater treatment systems

When organic matter enters a water body, it will be oxidized and decomposed under the action of microorganisms, causing the dissolved oxygen in the water to gradually decrease. When the oxidation process is too fast, and the water body cannot absorb enough oxygen from the atmosphere in time to replenish the consumed oxygen, the dissolved oxygen in the water may drop very low (such as below 3~4mg/L) This will affect the normal growth of aquatic organisms. When the dissolved oxygen in the water is exhausted, the organic matter begins anaerobic digestion, producing odor, and affecting environmental sanitation.

        Since the organic matter contained in wastewater is often a very complex mixture of multiple components, it is difficult to determine the quantitative values of various components one by one. In practice, some comprehensive indicators are often used to indirectly characterize the amount of organic matter in water. There are two types of comprehensive indicators that represent the content of organic matter in water. One type is the oxygen demand equivalent to the amount of organic matter in water (O2) indicators, such as biochemical oxygen demand BOD chemical oxygen demand COD and total oxygen demand TOD etc. ; Another type is the carbon (C) indicators, such as total organic carbon TOC For the same type of wastewater, the values of these indicators are generally different, and the order of magnitude is TOD>CODCr>BOD5>TOC

Excessive biochemical oxygen demand

        The full name of biochemical oxygen demand is Biochemical Oxygen Demand abbreviated as BOD It represents the amount of dissolved oxygen consumed in the biochemical oxidation process of microorganisms decomposing organic matter in water at a temperature of 20℃ and under aerobic conditions, that is, the amount of oxygen required for the stabilization of biodegradable organic matter in water, the unit is mg/L。 BOD It not only includes the oxygen consumed by the growth and reproduction or respiration of aerobic microorganisms in water, but also includes the oxygen consumed by reductive inorganic substances such as sulfides and ferrous iron, but the proportion of this part is usually very small. Therefore, BOD The larger the value, the more organic matter in the water.

        When soluble organic matter is consumed by bacteria, it is converted into carbon dioxide and biological flocs, and then settled from the effluent. Reducing the organic matter content of the effluent and improving BOD level, the mentioned process is a popular method of control BOD by promoting " food ” and the correct balance of organic matter. This can be achieved by appropriate aeration methods, where air is introduced into the effluent to increase the rate of this biological oxidation, which in turn increases the level of settleable solids, which can then be removed from the effluent by methods such as filtration or clarification.

Excessive total suspended and dissolved solids

        Depending on the TSS and TDS levels in wastewater and different emission standard levels, the implementation methods will be different. Commonly used methods to reduce TSS Treatment methods: coagulation, flocculation, sedimentation, sand or carbon filtration.

TDS reduction is a more complex process. If the pollutants are metal-based, such as calcium, magnesium or iron, simple chemical additives can be added during the clarification process to reduce these pollutants. If it is sodium, chlorine or other highly soluble ions, desalination or evaporation processes may be required.

Excessive nitrates and phosphates

        When large amounts of nitrates or phosphates are not removed from wastewater, and these nutrients are discharged into the local environment, they will increase BOD leading to widespread weed growth, algae and phytoplankton, leading to water deoxygenation, killing organisms and potentially causing hypoxia. They can enter wastewater streams in various ways, including human and food waste, detergents and pesticides.

        If the wastewater treatment system does not meet the nitrate and phosphate discharge levels, the following methods may be useful:

        Nitrate removal: Nitrates can be removed by several methods, including ion exchange, reverse osmosis or conventional biological treatment and denitrification.

        Phosphate removal: An effective method for removing phosphates from wastewater streams is usually coagulation / chemical precipitation, depending on the type of phosphate present.

Wastewater contains oil and grease

        Oil and grease are " hydrophobic ” They tend to repel from water and adhere to surfaces without water. A large amount of grease in wastewater will clog sewers and drains, damage human health and kill aquatic organisms. Grease is also often introduced into wastewater as a byproduct of food production. These pollutants are strictly regulated and must not be discharged with wastewater.

        Wastewater containing grease needs to use a dissolved air flotation machine ( DAF The device uses pressure to dissolve air in water to remove oil. When bubbles float to the surface, they attach to the oil and grease, allowing them to be skimmed from the top. Another successful method for removing oil and grease involves certain types of filters, such as ultrafiltration or activated carbon.