Wastewater is a complex system composed of water and various impurities, which is represented by water quality indicators. Water quality indicators can be divided into physical indicators, chemical indicators and biological indicators. Various water quality indicators can indicate the types and quantities of impurities in water, and can judge whether the water quality is good or bad and whether the discharge indicators are met.

Physical indicators of wastewater mainly include temperature, color, odor and solid content. Chromaticity and solid content are often detected.

1. Chromaticity Food industry wastewater often contains organic matter or inorganic dyes, biological pigments, inorganic salts, organic additives and so on, but wastewater is colored, and the color is very deep. In water quality analysis, the index to measure the degree of water color is chroma. In general, the true color after removal of suspended solids is taken as the standard. The colorimetric analysis method is used to compare the color of the standard colored solution of known concentration with that of the water sample of unknown colority.

2. Most of the magazines in wastewater with solid content belong to solid substances. These solid substances exist in water in the form of dissolution and suspension. They are called total solids, including organic compounds, inorganic compounds and various organisms. In water quality analysis, besides the determination of total solid content, several indicators such as suspended solids, volatile suspended solids and dissolved solids should also be determined.

(1) Total Solid (TS) refers to the residue of a certain amount of water sample dried at 105-110 C in water quality analysis, which is expressed by weighing.

(2) Suspended solids (SS) or suspended solids are the parts of total solids in suspended state, which contain organic and inorganic components.

(3) Volatile suspended solids (VSS) are the weight loss of suspended solids by heating and burning at 600 (?) C, representing the organic part of suspended solids, one of which is biodegradable suspended solids (BVSS) and the other is non-biodegradable (NBVSS).

(4) Non-volatile suspended solids (NVSS) is the residual part of suspended solids after burning, also known as ash, which represents the inorganic part of suspended solids.

(5) Dissolved solids (DS) or dissolved solids refer to the dissolved part of the total solids, which is obtained by drying and weighing a certain amount of filtrate of water samples.