In fact, water quality issues have long been a focus of attention, and wastewater treatment has now become a key priority in China’s environmental governance. However, due to the diversity of wastewater types, treatment methods vary accordingly. This article, in collaboration with a Wastewater Monitoring Equipment Manufacturer, provides a brief overview of the sources of domestic, paper-making, and dyeing wastewater.

Domestic Wastewater

Domestic wastewater is primarily generated from the post-use discharge of households, commercial establishments, and urban public facilities. As this wastewater undergoes gradual decomposition, its dissolved oxygen (DO) content decreases, triggering anaerobic reactions that produce hydrogen sulfide, ska-tole, and other compounds—resulting in persistent foul odors.

Pollution Characteristics of Domestic Wastewater

1. Elevated levels of nitrogen, phosphorus, and sulfur;
2. Odor-causing substances: Carbohydrates, fats, cellulose, and proteins, which are metabolized by anaerobic bacteria to generate malodorous compounds;
3. Pathogenic contaminants: Including microorganisms and pathogens, which bring certain risks of transmitting infectious diseases to humans;
4. Detergent-related hazards: Excessive use of detergents leads to elevated detergent concentrations in wastewater, which are harmful to human health.

Paper-making Industry Wastewater

Paper-making wastewater originates from the pulping process, where raw materials (e.g., wood, reeds, rags) are subjected to high-temperature and high-pressure cooking to extract cellulose. During this process, non-cellulose components in the raw materials are discharged as paper-making “black liquor”, which contains volatile organic acids, lignin, and cellulose—exhibiting strong odor and high polluting potential.

Hazards of Paper-making Wastewater

Black liquor is highly hazardous, accounting for 90% of total wastewater discharge in the paper-making industry. It is characterized by high alkalinity, dark color, excessive foaming, and pungent odor, and it consumes large amounts of dissolved oxygen in water bodies, causing obvious water pollution and considerable harm to both the environment and human health. Additionally, chlorine-containing wastewater (e.g., chlorinated and hypochlorite bleaching effluents) is generated during disinfection and bleaching processes. These effluents contain carcinogenic substances, and improper disinfection behaviors bring notable threats to human health and ecological systems.

Dyeing Wastewater

Dyeing wastewater is categorized based on production processes, as follows:

1. Desizing wastewater: Contains acids, starch, alkali’s, and enzymes; characterized by small volume but high pollutant concentration;
2. Scouring wastewater: Contains oils, alkali’s, surfactant, cellulose, fruit acids, and nitrogenous compounds; features large volume and high pollutant concentration;
3. Bleaching wastewater: Contains residual bleaching agents (e.g., residual chlorine), trace acetic acid, and sodium sulfate;
4. Mercerizing wastewater: Highly alkaline with high sodium hydroxide (Na-OH) content. In dyeing plants, Na-OHis recovered via evaporation and concentration, so the discharged wastewater remains strongly alkaline with high biochemical oxygen demand (BOD) and chemical oxygen demand (COD);
5. Dyeing wastewater: Variable in composition, with high chroma, low suspended solids (SS), and high BOD/COD—indicating poor biodegradability;
6. Printing wastewater: High in BOD, COD, and paste content;
7. Finishing wastewater: Contains resins, formaldehyde, and sizing agents; small in volume;
8. Alkali reduction wastewater (from polyester silk-like fabric production): Contains ethylene glycol and terephthalic acid (accounting for about 75% of the total content).

General Characteristics of Dyeing Wastewater

Dyeing wastewater is marked by large volume, high alkalinity, high organic pollutant content, and obvious fluctuations in water quality.

Monitoring of Harmful Substances in Wastewater

To determine the concentration of harmful substances in wastewater, real-time parameter monitoring is required. For example, residual disinfectants (e.g., total residual chlorine) from bleaching and disinfection processes can be detected using an Online Total Residual Chlorine Analyzer. Similarly, different parameters should be monitored using corresponding water quality monitoring equipment.