Municipal Wastewater Treatment
So far, there have been no substantial studies assessing the impact of mature constructed wetlands on the treatment performance based on efficiency comparisons with new treatment systems without fixed media such as artificial ponds. This chapter fills gaps in knowledge and understanding by evaluating the capability of mature wetlands dissimilar in their designs and operations in producing effluent that is treated appropriately before release into the environment by comparing their efficiency with a new treatment system comprising different types of artificial ponds.
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Three types of new artificial ponds were chosen in this study to assess the impact of mature wetland plants and the corresponding biofilm that developed around the gravel on nutrient removal and water quality. Various researchers including Kadlec and Wallace , Vymazal , and Scholz , have reviewed the effectiveness of constructed vertical-flow wetlands used for the treatment of urban wastewater.
However, the impact of mature reeds subjected to long-term studies within constructed wetlands and passive aeration by operating them in tidal-flow mode on the long-term treatment efficiency has been less well researched. Therefore, there is the research need to focus on the effect of reeds and aeration on the treatment performance of both mature wetlands and ponds.
A comparison between the nonaerated ponds, the actively aerated ponds and the mature wetlands would allow for the assessment of the impact of passive aeration of wetland systems on water quality parameters. Seshadri, in Environmental Materials and Waste , P coming from both domestic and industrial sources enters municipal wastewater treatment plants. Loads of P from various sources such as human waste 0.
P present in wastewater is commonly recovered by chemical coagulation or biological P removal. The small 0. MBR technology was selected due to spatial constraints on the site combined with the requirement to meet stringent discharge water quality standards. Pre-treatment at the plant comprises equalization for 4. Scouring air is provided at a rate of 0. Aeration incurs an energy demand of 0. In the United States, land application of municipal wastewater and biosolids has been practiced for its beneficial effects and for disposal purposes since the advent of modern wastewater treatment about years ago.
By , about 50 farms were using land treatment in England, and many other farms were being used close to other major cities in Europe. In the United States, sewage farms were established by about Municipal sludge in Ohio was used as a fertilizer as early as Since the early s, more emphasis has been placed on applying sludge to cropland at rates to supply adequate nutrients for crop growth Hinesly et al.
In the s and 80s, many studies were undertaken to investigate the potential benefits and hazards of land application, in both the United States and Europe. Ultimately in , U. The distinction between sewage sludge and biosolids is described in Information Box Sewage sludge : the solid, semisolid, or liquid residue generated during the treatment of domestic sewage in a treatment works.
Biosolids : two different definitions have been developed:. EPA : the primarily organic solid product yielded by municipal wastewater treatment processes that can be beneficially recycled whether or not they are currently being recycled. NRC National Research Council , : sewage sludge that has been treated to meet the land application standards in the Part rule or any other equivalent land application standards or practices. Adapted from EPA U. Environmental Protection Agency : A guide to field storage of biosolids and the organic by-products used in agriculture and for soil resource management.
Currently, most land application of biosolids in the United States utilizes Class B biosolids. However, due to public concerns over potential hazards, in some areas of the United States, land application of Class B biosolids has been banned. A recent report indicates that approximately million farmers worldwide grow crops in fields fertilized with human waste IWMI, AFOs are defined as a feedlot or a facility where animals are kept for greater than 45 days; cattle grazing on pasture are exempt EPA, CAFOs are then designated based on numerical criteria such as greater than cattle or broiler chickens EPA, Since the s, the vast majority of animals raised for food and their products are produced in CAFOs.
For all AFO and CAFO food animal production, it has always been the responsibility of the owner to dispose of the manure, with reliance on disposal to nearby fields, thereby keeping costs low. Manure land application has not been governed by any specific law or federal regulation; however, guidelines exist for suggested rates of manure for land application based on nutrient requirements, typically N or P, of the crop to be grown.
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Most states require nutrient management plans to be established prior to the establishment of a new CAFO. These plans essentially establish how the CAFO owner will dispose of the manure in both a quantitative i. Thus far, the level of scrutiny reserved for biosolids land application has not been similarly applied to manure. Increase in CAFO size necessitated revision of the regulations in The rule was challenged, and now an AFO can apply for an exception provided that the manure can be appropriately stored to prevent accidental release i.
These limits and rules are specifically designed to reduce discharge to surface water and do not govern the land application of manure to soil, unless there is a threat of effluent runoff to surface water. Apart from these rules and guidelines, there are no other regulations for land application of manure. Biosolids and manure are applied to agricultural and nonagricultural lands as a soil amendment because they improve the chemical and physical properties of soils, and because they contain nutrients for plant growth. Land application on agricultural land is used to grow food crops such as corn or wheat, and nonfood crops such as cotton.
Nonagricultural land application includes forests, rangelands, public parks, golf courses, and cemeteries. Biosolids and manure are also used to revegetate severely disturbed lands such as mine tailings or strip mine areas. A simplified schematic of how biosolids are produced is presented in Fig. Class A biosolids are treated to reduce the presence of pathogens to below detectable levels and can be used without any pathogen-related restrictions at the application site. Class A biosolids can also be bagged and sold to the public.
Class B biosolids are also treated to reduce pathogens, but still contain detectable levels of them. Class B biosolids have site restrictions to minimize the potential for human exposure, until environmental factors such as heat, sunlight, or desiccation have further reduced pathogen numbers. Class B biosolids cannot be sold or given away in bags or other containers or used at sites with public use.
Simplified schematic of biosolids production. In many cases, effluent water from one process can be suitable for reuse in another process if given suitable treatment. This can reduce costs by lowering charges for water consumption, reduce the costs of effluent disposal because of reduced volume and lower energy costs due to the recovery of heat in recycled wastewater. Industrial water treatment seeks to manage four main problem areas: scaling , corrosion , microbiological activity and disposal of residual wastewater.
Boilers do not have many problems with microbes as the high temperatures prevent their growth. Scaling occurs when the chemistry and temperature conditions are such that the dissolved mineral salts in the water are caused to precipitate and form solid deposits. These can be mobile, like a fine silt, or can build up in layers on the metal surfaces of the systems. Scale is a problem because it insulates and heat exchange becomes less efficient as the scale thickens, which wastes energy.
Scale also narrows pipe widths and therefore increases the energy used in pumping the water through the pipes. Corrosion occurs when the parent metal oxidises as iron rusts, for example and gradually the integrity of the plant equipment is compromised.
The corrosion products can cause similar problems to scale, but corrosion can also lead to leaks, which in a pressurised system can lead to catastrophic failures. Microbes can thrive in untreated cooling water, which is warm and sometimes full of organic nutrients as wet cooling towers are very efficient air scrubbers. Dust, flies, grass, fungal spores, and others collect in the water and create a sort of "microbial soup" if not treated with biocides.
Template:Heavy metal removal certain processes like tanning and paper making use heavy metals such as Chrome for tanning. Although most is used up but some amount remains and gets carried away with water. The presence in drinking water is toxic when consumed so even the smallest amount must be removed.
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The definitions are important because they limit the methods of sludge management. The most important definitions of sewage sludge are listed in Table 1. Definitions of sewage sludge according to various legal acts. Sewage plants treating domestic or urban wastewater and from other sewage plants treating wastewaters of a composition similar to domestic and urban wastewaters.
Residual sludge from septic tanks or other similar installations for the treatment of sewage. Based on the definitions above, it can be stated that sewage sludge definitions include both municipal and industrial sludge; however the regulations concerning municipal sludge are more frequent.
Municipal sludge is produced in municipal wastewater treatment plants WWTPs and it contains a lot of human excreta. Fecal excreta are also a component of fecal sludge. Sewage and fecal sludge contain organic matter and nutrients and because of this they can be used as a soil conditioner or a medium-grade soil fertilizer Guidelines, The soil application of sewage sludge may improve the nutrients availability for plants for a longer period of time than artificial fertilizers Grobelak et al.
To the risks related to the use of sewage sludge in agriculture, the presence of pathogens, such as bacteria, viruses, helminthes, or protozoa as well as contamination by organic and inorganic micropollutants can be accounted Guidelines, The pH of the sewage sludge is normally ranged 6. The heat value of the dry sludge is about Sludge also contains other elements such as potassium, magnesium, sulfur, and minor plant nutrients Sewage Sludge, ; Kijo-Kleczkowska et al.
These kinds of sludge can be treated in a similar way. Industrial sludge has very diversified physicochemical properties, for example, it can contain toxic compounds and elements at very high concentrations. Sludge management methods, which are regulated by law, can be recovery, disposal, recycling, or treatment. Recovery means any operation the principal result of which is waste serving a useful purpose by replacing other materials that would otherwise have been used to fulfill a particular function, or waste being prepared to fulfill that function in the plant or in the wider economy.
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Recycling means any process of recovery in which waste materials are reprocessed into products, materials, or substances, whether for the original or other purposes. It includes the reprocessing of organic material, but does not include energy recovery and reprocessing into materials that are to be used as fuels or for backfilling operations. Disposal means any operation that is not recovery, even where the operation has a secondary consequence that is the recovery of substances or energy.