The pollution index, abbreviated as SDI, is one of the important parameters of water quality indicators!

The currently effective RO/NF system may have colloidal contamination in the inlet water. The best technique is to measure the sedimentation density index of the inlet water, which is an important parameter that must be determined before RO design. During RO operation, regular measurements must be taken, and ASTM D4189-82 specifies the standard for this test. The inlet requirement for membrane systems is SDI ≤ 5. Effective techniques for reducing SDI preprocessing include multi-media filters, ultrafiltration, etc. Adding a polyelectrolyte before filtration can sometimes enhance the ability of physical filtration and reduce SDI values.

(1) The process of microorganisms decomposing organic matter in surface water consumes the amount of dissolved oxygen in the water, which is called biochemical oxygen demand and is usually recorded as BOD.

(2) The amount of oxidant consumed during the chemical oxidation process of substances that can be oxidized in water under specified conditions, expressed in milligrams of oxygen consumed per liter of water sample, is usually referred to as COD.

COD is the amount of oxidant consumed when using a certain strong oxidant to treat wastewater under certain conditions. It reflects the degree of material pollution in water, and the higher the chemical oxygen demand, the more severe the pollution of organic matter in water. The close relationship between BOD and COD refers to the mass concentration of dissolved oxygen required for the biochemical process of microbial decomposition of organic matter in water under aerobic conditions. In order to make the BOD detection values comparable, a time period is generally specified and the dissolved oxygen consumption in water is measured. Generally, a five-day period is used, called five-day biochemical oxygen demand, denoted as BOD5, which is often used. The higher the BOD value, the more organic matter is present in the water, and therefore the more severe the pollution. BOD is an environmental monitoring indicator used to monitor the pollution of organic matter in water. Organic matter can be decomposed by microorganisms, which requires oxygen consumption. If the dissolved oxygen in the water is insufficient to meet the needs of microorganisms, the water will be treated for pollution. The reclaimed water reuse system in sewage treatment can use ultrafiltration equipment to reduce COD and BOD in wastewater.

refers to solid substances suspended in water, including insoluble inorganic and organic matter, as well as mud, sand, clay, microorganisms, etc. Suspended solids are the main cause of water turbidity. Organic suspended solids in water are prone to anaerobic fermentation after precipitation, leading to deterioration of water quality. The comprehensive sewage discharge standards in China are divided into three levels, which stipulate the high allowable discharge concentration of suspended solids in sewage and wastewater. The quality standards for groundwater and the hygiene standards for drinking water in China stipulate the turbidity of suspended solids in water as the indicator.