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.

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.

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是在特定条件下使用某种强氧化剂处理废水时消耗的氧化剂量。它反映了水中物质污染的程度，化学需氧量越高，水中有机物的污染就越严重。BOD和COD之间的密切关系指的是在好氧条件下水中有机物的微生物分解的生化过程所需的溶解氧的质量浓度。为了使BOD检测值可比较，通常会指定一个时间段并测量水中的溶解氧消耗量。通常使用五天的时间段，称为五天生化需氧量，表示为BOD5，经常使用。BOD值越高，水中的有机物质越多，因此污染越严重。BOD是用于监测水中有机物污染的环境监测指标。有机物可以被微生物分解，这需要消耗氧气。如果水中的溶解氧不足以满足微生物的需求，水将被处理以减少污染。污水处理中的回用水系统可以使用超滤设备来减少废水中的COD和BOD。

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.