Waste Water Management
- Water, food and energy securities are emerging as increasingly important and vital issues for India and the world.
- Most of the river basins in India and elsewhere are closing or closed and experiencing moderate to severe water shortages, brought on by the simultaneous effects of agricultural growth, industrialization and urbanization.
- Current and future fresh water demand could be met by enhancing water use efficiency and demand management. Thus, wastewater/low quality water is emerging as potential source for demand management after essential treatment.
- An estimated 38354 million litres per day (MLD) sewage is generated in major cities of India, but the sewage treatment capacity is only of 11786 MLD.
- Similarly, only 60% of industrial waste water, mostly large scale industries, is treated.
- Performance of state owned sewage treatment plants, for treating municipal waste water, and common effluent treatment plants, for treating effluent from small scale industries, is also not complying with prescribed standards. Thus, effluent from the treatment plants, often, not suitable for household purpose and reuse of the waste water is mostly restricted to agricultural and industrial purposes.
- Wastewater- irrigated fields generate great employment opportunity for female and male agricultural labourers to cultivate crops, vegetables, flowers, fodders that can be sold in nearby markets or for use by their livestock.
- However, there are higher risk associated to human health and the environment on use of wastewater especially in developing countries, where rarely the wastewater is treated and large volumes of untreated wastewater are being used in agriculture.
What is wastewater?
- Wastewater or sewage is the byproduct of many uses of water. There are the household uses such as showering, dishwashing, laundry and, of course, flushing the toilet. Additionally, companies use water for many purposes including processes, products, and cleaning or rinsing of parts.
- After the water has been used, it enters the wastewater stream, and it flows to the wastewater treatment plant.
- When people visit a treatment plant for the first time, often it is not what they perceived it would be. These wastewater plants are complex facilities and provide a high quality end product.
Why treat wastewater?
- We need to remove the wastewater pollutants to protect the environment and protect public health. When water is used by our society, the water becomes contaminated with pollutants.
- If left untreated, these pollutants would negatively affect our water environment. For example, organic matter can cause oxygen depletion in lakes, rivers, and streams.
- This biological decomposition of organics could result in fish kills and/or foul odors. Waterborne diseases are also eliminated through proper wastewater treatment.
- Additionally, there are many pollutants that could exhibit toxic effects on aquatic life and the public.
How do we collect the wastewater?
- The sewer or collection system is designed so that it flows to a centralized treatment location.
- The collection system is comprised of smaller sewers with a diameter of about four inches.
- As more homes and companies are connected along the system, the pipes become larger in diameter.
- Where gravity systems are not practical, pumping stations are often included to lift the wastewater.
What is Primary Treatment?
- Primary treatment is a physical settling process that removes solids. Wastewater that enters the primary settling tank (or clarifier) is slowed down to enable the heavier solids to settle to the bottom.
- Lighter materials, such as grease, will float to the top of the tank. Settling tanks are designed with mechanisms to remove both the settled solids, as well as the floating solids. Primary clarifiers are either circular or rectangular.
- Both types work equally well when properly designed and maintained. Not all plants have primary treatment. Primary treatment generates primary sludge.
- The sludge is removed and pumped to the solids treatment process for ultimate removal.
What is Secondary Treatment?
- Secondary treatment is a biological treatment process used to stabilize the dissolved solids.
- Microorganisms (e.g., bacteria) feed on the organic solids (food) in the wastewater and convert the organics into a cellular or biological mass that can later be removed.
- These biological processes are aerobic processes. Oxygen must be provided for these aerobic organisms to work properly and efficiently. An integral part of secondary treatment processes is another set of settling tanks or clarifiers.
- These secondary clarifiers (final clarifiers) remove the biological mass that has grown during biological treatment.
What comes after Secondary Treatment?
- In many plants, the next process is called disinfection. Disinfection means the inactivation of disease-causing organisms.
- It is sometimes confused with sterilization which means the killing of all organisms.
- In disinfection, the wastewater following secondary treatment is usually treated in one of two ways: (1) chlorination or (2) ultra-violet radiation.
Chlorination
- Chlorination involves the use of chlorine, either in the form of a gas (less common today), or as a liquid (sodium hypochlorite).
- The chlorine oxidizes the microorganisms. The effectiveness of this process is monitored by testing the fecal coliform group.
- This indicator group of microorganisms are easy to grow in a laboratory and are tougher to kill than pathogens. Some chlorination systems also have dechlorination systems to remove any residual chlorine.
Ultraviolet (UV) disinfection systems
- Ultraviolet (UV) disinfection systems contact the treated secondary wastewater with UV light bulbs that are encased in clear housings.
- The UV light kills pathogenic organisms by using a germicidal photochemical wavelength.
- Unlike chlorination, UV leaves no residual in the wastewater with which to be concerned.
- Plants that use UV must either have dual UV systems or have chlorination as a backup. Additionally, these UV systems are energy consumptive.
What is Advanced Treatment?
- Some treatment plants may be required to remove nutrients (nitrogen and phosphorus) due to the possible negative impacts on the receiving stream (e.g., ammonia toxicity to fish).
- Advanced treatment processes are used to remove nutrients, additional solids, and/ or biochemical oxygen demand.
- Advance treatment provides a very high level of treatment that goes beyond secondary treatment.
- In the case of nitrogen removal, the processes are biological. For phosphorus removal, chemical additives are normally required.
Policy and Regulatory Framework for Wastewater
- Wastewater shares the policy and regulatory framework with water; however with some differences such as the role of bodies such as the Central Pollution Control Board (CPCB) becomes more critical.
- The CPCB, under the MoEF, is an advisory body to the government for prevention and control of water and air pollution and for improvement in air quality. At the state level, the state departments of environment and forests with the advice and assistance of the state pollution control boards (SPCBs) are responsible for enforcing the environmental acts and rules, and monitoring them.
- Meanwhile, many ad hoc expert appraisal committees (at the centre and state level) play a significant role in the grant of environmental clearances.
- Research is being conducted on applications of bio-technology on the treatment of industrial effluents – especially for paper and pulp industry, electroplating, distillery, tannery, dye and refineries – and biosensors for detection of pollutants, especially residues of pesticides and bio-diversity.
- Regulatory frameworks for on-site systems are virtually non-existent in India.