Wastewater Treatment
Introduction
Wastewater in general, and industrial wastewater in particular, constitute an ecological menace: It involves undesirable substances that must be disposed of and treated quickly and effectively. Conversely, untreated wastewater can cause serious problems, including damage to both human health and the environment. A plant or a business owner, who does not treat his or her wastewater is likely to incur rather steep penalties. Wastewater treatment is necessary in order to comply with regulations and prevent environmental hazards, even, at times, physical harm. Several technologies, designed to provide wastewater treatment are available, which have been in use around the world. Due to the distinct importance concerning the matter, a great deal of regulation now affects it. It is a field that is constantly evolving. Below, a list of the various methods for current wastewater treatment.
The result obtained after wastewater treatment process is called effluent. The effluent can be of diverse qualities, depending on its composition, its origin and the treatment process itself. It is the quality of the effluent that determines its potential usage. There are different levels of effluent quality allowed for agricultural irrigation, according to the crops' type and their mode of cultivation.
Wastewater Treatment Technologies
Pre-Treatment Processes
1. Wastewater Screener – A device used in order to separate coarse solids. It has crisscross bars or a mesh that are cleaned either mechanically or manually. In order to avoid the irritation poised by bad odors, since the effluent can reach a wastewater treatment plant in septic conditions, it is advisable to use a closed system.
2. Sand Sedimentation and Sludge Settlement - This is done in order to protect the equipment downstream from blockages or damage. Thus, it is necessary to create additional sedimentation for the heavy components before they initial treatment commences.
3. Equalizing Basin – It enables treatment using varying flow rates, which improves the performance of the settling basins and the biological treatment process. In addition, such basin could reduce the size of the treatment facilities required. It can also be used as an emergency reservoir in case of excess flow of effluent or the discharge of toxic substances into the wastewater.
Primary Wastewater Treatment Processes
Physical Sedimentation
Physical sedimentation is done in either a rectangular or a round sedimentation basin, with different flow regimes, in order to keep away floating solids. Primary physical sedimentation is designed to keep away floating solids, biological materials, oily substances, heavy metals, phosphorus and nitrogen. The relevant removal values are low as compared to the removal values obtained in a chemical precipitation. On the other hand, physical sedimentation does not pose difficulties at the biological treatment stage which occurs later in the process. In addition, its current operating costs are significantly lower (as compared to the cost of chemical precipitation).
Chemical Precipitation
This process is performed by adding chemicals that improve physical sedimentation. The dosage and type of chemicals should be examined by environmental consulting companies, after performing applicable laboratory tests. Sutok specializes in performing such tests for its customers.
The chemicals are placed in a mixing tank on top of the sediment, in order to ensure the rapid blending phase. The removal percentages are much higher than normal sedimentation without chemicals. In addition, the process allows the removal of phosphorus and heavy metals.
On the other hand, it is a more expensive process that involves the use of chemicals, which bring to the fore certain safety requirements attendant the process that are less suitable when combined with biological treatment, in addition to the resulting need for the removal of heavier sludge.
Secondary Wastewater Treatment
Aerobic Biological Treatment
This is a process where oxygen is released and is made available to bacteria that decompose the organic matter in the effluent. Aerobic reactors are highly effective and the resultant decomposition rates are much higher than those of anaerobic reactors. The main decomposition products are carbon dioxide (CO2) and water.
The most common relevant method of operation is called "activated sludge."
It should be noted, that biological processes suffer a significant disadvantage due to their high sensitivity to environmental conditions: pH level, temperature, salinity, toxicity, presence of heavy metals, and others.
Anaerobic Biological Treatment
To remove nitrogen from wastewater treatment facilities, it is generally customary to combine anaerobic and anoxic conditions. Note, that a biological reactor, operating under anaerobic conditions, is only suitable for treating wastewater solely from an organic source.
Such reactor has several advantages:
Low-level production of excess sludge, low nutrients' requirement, methane is an end product which can be utilized as an energy resource. The process itself consumes no energy. Usually, when the organic loads are high, a switch is made to using an anaerobic biological reactor instead of the aerobic one.
A notable disadvantage of this type of treatment is the slow decomposition rate and sulfide production, as a result. Factors affecting the process are: temperature, pH level, ammonia concentrations, sulfide, and more.
The combination of aerobic biological and anaerobic or anoxic treatments enables the removal of nitrogen and phosphorus both effectively and inexpensively.
Wastewater Treatment in Constructed Wetlands
A treatment method which is once again raising interest is one in which wastewater treatment is accomplished by using constructed wetlands.
Constructed wetlands are an artificial wet system, designed to treat both water and wastewater. The method usage is rather widespread throughout the world, especially in rural areas. In Israel, however, it has hardly been used; it can be observed, among others, in Harduf and Neot Smadar in Israel.
The system upgrades water quality based on natural microbiological, biological, physical and chemical processes occurring therein. In constructed wetlands the effluent is made to flow using various methods either above or below the surface, then "nature" does its thing. In other words, the process is based on natural energy and environmental resources such as solar energy, soil, plants and bacteria. The habitat uses the available organic matter in order to amass biomass.
The purification process may be divided into three categories:
1.Biological processes, carried out by bacteria that form a biofilm on the substrate, or by placing bacteria in the root system, which include resulting photosynthesis, cellular respiration, fermentation, simultaneous nitrification-denitrification and microbial phosphorus removal.
2.Chemical processes, which include chemical reactions among various factors, including heavy metals, solubility of metals and nutrients, oxidation-redox reactions, transformation and ion exchange.
3.Physical processes, which include sedimentation/precipitation or adsorption of solid materials, filtration and gravitational precipitation.
Constructed wetlands require the usage of conventional primary treatment systems to affect both solids' removal as well as that of primary sludge, in order to prevent blockages, etc. However, today there is a method available that allows such system to function even without an initial treatment.
Advantages: Low construction cost, as compared to a mechanical wastewater treatment plant. Cost of operation and maintenance of a constructed wetland system is extremely low (significant substrate treatment is required every 5-10 years and sometimes at even longer intervals). Operation is very easy and skilled manpower is not required. Other than the use of pumps, there is no energy consumption involved; moreover, the technology is very safe. In addition, constructed wetlands are placed underground and therefore no ill-effects are at issue. Such system contributes greatly to environmental aesthetics, since it contains green vegetation surfaces, while avoiding the use of concrete and bulky mechanization. It is important to note that the use of constructed wetlands prevents the formation and thus eliminates the need for secondary sludge treatment, which spares resources rather significantly.
Disadvantages: The land area required for housing and operating such a system is very high and therefore not suitable for large localities, especially in crowded places such as Israel. In addition, there are difficulties due to regulatory and approval requirements, brought about by three factors: The ease of designing a conventional intensive system, the perception of constructed wetland technology as inferior when compared to the intensive methods and the lack of relevant procedures and guidelines.
Tertiary Wastewater Treatment
Complementary treatment, which may include additional treatment of nitrogen and phosphorus, along with the separation of residual organic matter and remnants of suspended solids. Technologically, such system has a wide range of technologies including, filtration, adsorption, complementary biological treatment, disinfection and more. Tertiary treatment is highly important, as it is the last step in refining the effluent, before is departs the treatment facility.
In Conclusion
The world of wastewater treatment is copious with groundbreaking technologies. Due to the variety of existing technologies and the great environmental and economic importance that wastewater treatment has, it is advisable to seek the help of professionals who know how to offer the most optimal treatment for wastewater, so that it can be accomplished efficiently and effectively and at the lowest costs.
Sutok Environmental Engineering has extensive experience in treating wastewater and industrial wastewater. It endeavors to provide its clients with the best treatment for wastewater, while correspondingly saving them substantial monetary outlays in their business operations.
