Domestic wastewater refers to wastewater discharged during daily life activities. This wastewater is mainly polluted by household waste and human excrement. The quantity, composition, and concentration of pollutants are related to people's living habits and water consumption. Domestic wastewater generally does not contain toxic substances; however, it provides suitable conditions for microbial reproduction and contains a large number of bacteria and pathogens, posing a certain degree of harm from a hygiene perspective.
Due to the continuous increase in urban population, the problem of urban domestic wastewater treatment is becoming increasingly prominent. Furthermore, due to outdated technology, funding shortages, and significant treatment difficulties, it has been impacting the urban environment and its development. If these problems are not addressed promptly, pollution will become more severe and its impact more detrimental as urbanization progresses and water consumption continues to increase.
Urban domestic wastewater differs from industrial wastewater, which can be controlled by stopping pollution or relocating industrial enterprises to address the source. Urban domestic wastewater mainly originates from households, schools, businesses, and other urban public places and facilities. The wide range and inevitability of its sources also lead to regional tendencies in wastewater treatment. Urban domestic sewage contains a wide variety of pollutants, but its main components are primarily organic matter, including starch, protein, sugars, and mineral oil from household waste. It also tends to have high levels of BOD2 (Biological Oxygen Demand), CODc2 (Chemical Oxygen Demand), TkN (Kjeldahl Nitrogen), TP (Total Phosphorus), and TN (Total Nitrogen). When discharged into water bodies, it easily causes eutrophication, leading to the proliferation of algae, which is related to red tides and algal blooms. When seasonal temperatures cause algae to die off, the water becomes stagnant and foul-smelling, further deteriorating the water quality. This understanding of the characteristics and specific components of urban domestic sewage has given us a clearer understanding of each stage of its treatment process.
We all know that water is the source of life, and my country is a country with relatively scarce freshwater resources. Saving urban drinking water is like saving our lives-it's urgent!
Industrial wastewater: Industrial production generates many types of pollutants, and the types and concentrations of pollutants produced by different industries vary significantly.
Electroplating wastewater: The main source of zinc in electroplating and metal processing wastewater is the drag solution from electroplating or pickling. Pollutants are transferred to the rinsing water during the metal rinsing process. The pickling process involves immersing the metal (zinc or copper) in a strong acid to remove surface oxides, followed by immersion in a brightener containing strong chromic acid for brightening.
This wastewater contains large amounts of hydrochloric acid, heavy metal ions such as zinc and copper, and organic brighteners, which are highly toxic. Some contain carcinogenic, teratogenic, and mutagenic substances, posing a significant threat to human health. Therefore, electroplating wastewater must be carefully recycled and treated to eliminate or reduce its environmental pollution.
Electroplating mixed wastewater treatment equipment consists of an equalization tank, a dosing tank, a reduction tank, a neutralization reaction tank, a pH adjustment tank, a flocculation tank, an inclined tube sedimentation tank, a chamber filter press, a clear water tank, an air flotation reactor, and an activated carbon filter.
Electroplating wastewater treatment employs an internal electrolytic treatment process using iron scrap. This technology primarily utilizes activated industrial waste iron scrap to purify wastewater. When the wastewater comes into contact with the packing material, electrochemical, chemical, and physical reactions occur, including catalysis, oxidation, reduction, displacement, co-precipitation, flocculation, and adsorption, removing various metal ions from the wastewater and thus purifying it.
Heavy Metal Wastewater: Heavy metal wastewater mainly originates from wastewater discharged by mining, smelting, electrolysis, electroplating, pesticide, pharmaceutical, paint, and pigment companies. If heavy metal wastewater is not treated, it will severely pollute the environment. The types, concentrations, and forms of heavy metals in wastewater vary depending on the production enterprise. Heavy metal removal is crucial in wastewater treatment.
Since heavy metals cannot be decomposed or destroyed, their removal can only be achieved by changing their location and physical and chemical forms. For example, in wastewater treatment, after chemical precipitation, heavy metals in the wastewater transform from dissolved ionic forms into insoluble compounds and precipitate, transferring from the water to the sludge. After ion exchange treatment, heavy metal ions in the wastewater transfer to the ion exchange resin, and after regeneration, they transfer from the resin to the regeneration waste liquid.
Therefore, the principles of heavy metal removal in wastewater treatment are:
Principle 1: The most fundamental approach is to reform production processes, avoiding or minimizing the use of highly toxic heavy metals.
Principle 2: Adopting reasonable process flows, scientific management, and operation to reduce the amount of heavy metals used and lost in wastewater, minimizing the amount of wastewater discharged. Heavy metal wastewater should be treated on-site at its source, without mixing with other wastewater to avoid complicating the treatment process. Furthermore, it should never be discharged directly into municipal sewers without heavy metal removal treatment to prevent the spread of heavy metal pollution.
Methods for removing heavy metals from wastewater can generally be divided into two categories: Method 1: This method transforms dissolved heavy metals in the wastewater into insoluble metallic compounds or elements, which are then removed through precipitation and flotation. Applicable methods include neutralization precipitation, sulfide precipitation, flotation separation, electrolytic precipitation (or flotation), and membrane electrolysis.
Method 2: This method concentrates and separates heavy metals in the wastewater without altering their chemical form. Applicable methods include reverse osmosis, electrodialysis, evaporation, and ion exchange. These wastewater treatment methods should be used individually or in combination, depending on the wastewater quality and quantity.
