Research and Analysis on Wastewater Treatment

  Wastewater treatment generally includes the following three levels of treatment: Primary treatment is mechanical treatment, such as bar screens, sedimentation tanks, or flotation machines, to remove stones, sand, grease, and oil from the wastewater. Secondary treatment is biological treatment, where pollutants in the wastewater are degraded and transformed into sludge by microorganisms. Tertiary treatment is advanced wastewater treatment, which includes nutrient removal and disinfection of the wastewater using chlorination, ultraviolet radiation, or ozone technology. Depending on the treatment objectives and water quality, some wastewater treatment processes may not include all of the above processes.

  1. Mechanical Treatment Section

  The mechanical (primary) treatment section includes structures such as bar screens, grit chambers, and primary sedimentation tanks. Its purpose is to remove coarse particles and suspended solids. The principle of treatment is to achieve solid-liquid separation through physical methods, separating pollutants from the wastewater using belt filter presses. This is a commonly used wastewater treatment method. Mechanical (primary) treatment is an essential part of all wastewater treatment processes (although some processes sometimes omit the primary sedimentation tank). The typical removal rates of BOD5 and SS in primary treatment of urban wastewater are 25% and 50%, respectively. In biological phosphorus and nitrogen removal wastewater treatment plants, aerated grit chambers are generally not recommended to avoid rapid degradation of organic matter. When the characteristics of the raw wastewater are unfavorable for phosphorus and nitrogen removal, the inclusion and method of primary sedimentation need careful analysis and consideration based on the specific water quality requirements of subsequent processes to ensure and improve the influent quality for phosphorus and nitrogen removal.

  2. Biological Wastewater Treatment

  Biological wastewater treatment is a secondary treatment process, primarily aimed at removing non-settleable suspended solids and dissolved biodegradable organic matter. Its processes are diverse, including activated sludge processes, AB processes, A/O processes, A2/O processes, SBR processes, oxidation ditch processes, stabilization pond processes, and land treatment methods. Currently, most urban wastewater treatment plants use the activated sludge process. The principle of biological treatment is to decompose organic matter and synthesize organisms through biological processes, especially the actions of microorganisms, transforming organic pollutants into harmless gaseous products (CO2), liquid products (water), and solid products rich in organic matter (microbial communities or biological sludge). Excess biological sludge is removed from the purified wastewater through solid-liquid separation in a sedimentation tank.