Energy from Sewage – Renewable energy to be tapped to make environment green:

Energy from Sewage – Renewable energy to be tapped to make environment green:

Sewage treatment, that is, the physical, chemical and biological processes used to clean industrial and domestic wastewater, has improved significantly over the past 20 years. However, the energy requirement to treat sewage to the highest standard has been quite large. Further tightening of water quality standards, especially in developed nations; suggest energy costs will increase substantially in future. We will discuss here about possibility of renewable energy generation from sewage, to offset the extra energy requirement for sewage treatment and also to use surplus energy for domestic purpose. In fact, the actual energy used will depend on the quality of sewage and intensity of treatment required.

A. Typically, there are three stages of treatment:

(a) Primary - Solids are physically settled out.

(b) Secondary - Bacteria convert organic matter to a carbon-rich sludge.

(c) Tertiary - Further treatment may be used to remove more organic matter and/or disinfect the water.

The effluent is generally discharged to fresh, ground or coastal water. Sludge is applied to agricultural land, incinerated, used for land reclamation or used for other purposes, such as composting or landfill etc.

B. In order to increase energy efficiency of water treatment and reuse of treated water few points have been discussed. By implementing these measures energy savings and efficiency of about 40% may be achieved:

(a) Choosing low-energy treatment options, if possible. However, local constraints may limit choice.

(b) Replacing machine parts, such as pumps and motors, with more efficient versions.

(c) Optimizing processes using sensor technology. For example, pumping can be adjusted according to flow.

(d) Reusing water. “Greywater” from bathing, laundry and washing dishes can be reused to flush WCs. This may provide savings of around a third of daily household water demand.

C. Energy generation - There are mature, widely-practiced technologies for generating fuels from sewage treatment. Moreover, research has identified future methods for exploiting sewage as an energy resource as well.

1. Current Technologies for Energy Production -

(a) Sludge Incineration - Most of the sewage sludge produced at sewage treatment plant is applied to agricultural land as a soil conditioner, reducing the need for fertilizer. Sludge may also be incinerated, with the option of energy recovery. However, to incinerate sludge, it must be dry enough to burn with no extra energy input other than that needed to fire up the incinerator. It therefore needs dewatering, using energy intensive processes such as centrifugation or thermal dehydration. Centrifugation requires less energy but surplus heat from incineration that can be used for thermal dehydration. There has been strong opposition from some sections of the public over incineration of wastes due to fears about impacts on human health. At present, reuse of sludge via application to land is generally considered a more acceptable option.

(b) Biogas - Biogas production from sewage sludge treatment, via a process called anaerobic digestion, is already a well established means of generating energy in many developed countries. Bacteria used to organic matter in sludge to produce a mixture of methane (CH4 of 60 – 65%), carbon dioxide (CO2 of 35 – 40%) and trace gases. Impurities, such as hydrogen sulfide and water, are removed and the resulting biogas is then commonly used in boilers or combined heat and power systems. Biogas may also be used for other applications, such as vehicle fuel, if CO2 is also removed. Anaerobic digestion also reduces the solids content of sludge by up to 30%, reducing the energy costs involved in its transport.

2. Future Technologies for Energy Production - There are several novel technologies that produce energy or fuel as a by-product of sewage treatment, although further work is needed to improve performance, reliability and cost-effectiveness.

(a) Conversion of sludge to oil and gas - Under carefully controlled conditions and extreme temperatures (450 – 1000 degree Celsius), sludge may undergo chemical reactions to produce fuels that may be used for energy production. Processes include gasification, which produces syngas (similar to natural gas), and pyrolysis, which produces bio-oil (similar to diesel oil). There is interest in these as potential alternatives to incineration of sludge. However, operational costs are high, particularly those of maintaining high temperatures, and conditions must be carefully controlled to prevent formation of harmful by-products, such as hydrogen cyanide.

(b) Biomass Crops - In some of the European countries, sewage sludge is applied as fertilizer to willow plantations. The trees are periodically coppiced and the wood used for fuel. Research into applying partially-treated, liquid sewage to biomass crops is also underway. Passage of the sewage through the soil acts as a final polishing step for treatment, degrading organic matter, reducing nitrogen and phosphorus and producing a cleaner effluent. Little energy is required and capital and operational costs are low. However, it is not yet known how efficient this system will be at removing pollution and there must be appropriate land available.

(c) Hydrogen from Sewage - There is much interest in hydrogen as a fuel, because it can be produced from a wide range of materials and provides power with minimal air pollution. Bacteria use organic matter to produce hydrogen by fermentation. However, applications for hydrogen, such as fuel cells, are not yet in widespread use.

(d) Microbial Fuel Cells - These devices offer the possibility of simultaneous sewage treatment and energy production, with water, CO2 and inorganic residue as by-products. Bacteria use organic matter to produce electricity. To date, only lab-scale microbial fuel cells have been developed in some of the developed countries that are able to power small devices.

D. Discussion on energy conservation and renewable energy in relation to sewage treatment system –

(a) Energy conservation is possible through the twin practices of efficient water use by consumers and efficient energy use by the water industry.

(b) There are well-established renewable energy options, such as biogas, and novel technologies, such as gasification, for sewage treatment. Many need further investment and research.

(c) Economic and water quality considerations are key drivers for the water industry. Integration of energy related objectives into the existing regulatory framework will be necessary.

Sewage disposal and its treatment – the ultimate recycling of used water:

Sewage disposal and its treatment – the ultimate recycling of used water:

In urban areas sewage is created by residences, institutions, hospitals and commercial and industrial establishments. Sewage treatment and disposal system is an important function for any city planner, in order to recycle the used water. It is the ultimate return of used water to the environment. Discharge to the environment must be accomplished without transmitting diseases, endangering aquatic organisms, impairing the soil.

Wastewater is treated to remove contaminants or pollutants that affect water quality. The treated wastewater is recycled / reused for gardening, irrigation, flushing etc. Disposal system has arrangements to distribute the used water either to aquatic bodies such as oceans, rivers, lakes, ponds, or lagoons or to land by absorption systems, groundwater recharge, and irrigation. Waste water must be mixed, diluted and absorbed before it is discharged to the general body of water, so that the receiving environments do not lose its beneficial usable characteristics; such as drinking, bathing, recreation, aquaculture, irrigation, groundwater recharge, industry etc.

Water quality standards relate to the esthetics and use of the receiving environment for public water supply, recreation, maintenance of aquatic life and wildlife, or agriculture. The parameters of water quality, which define the physical, chemical, and biological limits, include floating and settleable solids, turbidity, color, temperature, pH, dissolved oxygen, biochemical oxygen demand (BOD), toxic materials, heavy metals, and nutrients.

Sewage treatment is an artificial process to which sewage is subjected in order to remove or alter its objectionable constituents and to render it less dangerous from the standpoint of public health. It can be treated close to where it is created (in septic tanks, bio-filters or aerobic treatment systems), or may be collected and transported via a network of pipes and pump stations to a municipal treatment plant. Typically, sewage treatment involves three stages, called (a) primary, (b) secondary and (c) tertiary treatment.

(a) Primary sewage treatment removes larger floating objects through screening and sedimentation. The incoming wastewater flows through one or more screens and then enters a grit chamber where it slows down enough to allow sand, gravel, and other inorganic matter to settle out. In treatment plants where only primary treatment occurs, the effluent is chlorinated and discharged into circulation in a water source. The sludge, or sedimentation of larger solids, is removed, dried, and disposed of. Primary treatment removes 50 to 65 percent of suspended solids and decreases biological oxygen demand (BOD) by 25 to 40 percent. Primary treatment alone is not considered adequate for protection of the environment or people's health.

(b) Secondary treatment relates to processes similar to natural biological decomposition. Aerobic bacteria and other microorganisms are used to break down organic materials into inorganic carbon dioxide, water, and minerals. Trickling filters, which are made from a bed of rocks with a microbial covering, are used to absorb the organic material present in the water. Activated sludge processes can be used in place of trickling filters. The level of suspended solids and BOD in wastewater after primary and secondary treatment has been decreased by 90 to 95 percent. This level of treatment is not effective in removing viruses, heavy metals, dissolved minerals, or certain chemicals.

(c) Tertiary treatment is an advanced level of treatment. This form of treatment can decrease the level of suspended solids and BOD to approximately 1 percent of what was present in the raw sewage prior to primary treatment. Advanced treatment processes consist of several biological, chemical, or physical mechanisms. Sewage treatment aims to destroy pathogenic organisms. Since primary and secondary treatments do not destroy a significant number of organisms, chlorination, which is effective in killing bacteria, is used to disinfect treated effluent.

Most advanced wastewater treatment systems include denitrification and ammonia stripping, carbon adsorption of trace organics, and chemical precipitation. Evaporation, distillation, electro-dialysis, ultra-filtration, reverse osmosis, freeze drying, freeze-thaw, floatation, and land application, with particular emphasis on the increased use of natural and constructed wetlands, are being studied and utilized as methods for advanced wastewater treatment to improve the quality of the treated discharge to reduce unwanted effects on the receiving environment.

(d) Private sewage treatment, usually a septic system, is constructed on-site and is maintained by the private homeowner. In this case, the septic tank holds the solid materials while the water goes to a leach field or absorption field. The solids undergo decomposition, and on a regular basis, generally every three years, are pumped from the holding tank. This will vary according to use and capacity.

Water pollution by industries and its effects:

Water pollution by industries and its effects:

A change in the chemical, physical, biological, and radiological quality of water that is injurious to its uses. The term “water pollution” generally refers to human-induced changes to water quality. Thus, the discharge of toxic chemicals from industries or the release of human or livestock waste into a nearby water body is considered pollution.

The contamination of ground water of water bodies like rivers, lakes, wetlands, estuaries, and oceans can threaten the health of humans and aquatic life. Sources of water pollution may be divided into two categories. (i) Point-source pollution, in which contaminants are discharged from a discrete location. Sewage outfalls and oil spills are examples of point-source pollution. (ii) Non-point-source or diffuse pollution, referring to all of the other discharges that deliver contaminants to water bodies. Acid rain and unconfined runoff from agricultural or urban areas falls under this category.

The principal contaminants of water include toxic chemicals, nutrients, biodegradable organics, and bacterial & viral pathogens. Water pollution can affect human health when pollutants enter the body either via skin exposure or through the direct consumption of contaminated drinking water and contaminated food. Prime pollutants, including DDT and polychlorinated biphenyls (PCBs), persist in the natural environment and bioaccumulation occurs in the tissues of aquatic organisms. These prolonged and persistent organic pollutants are transferred up the food chain and they can reach levels of concern in fish species that are eaten by humans. Moreover, bacteria and viral pathogens can pose a public health risk for those who drink contaminated water or eat raw shellfish from polluted water bodies.

Contaminants have a significant impact on aquatic ecosystems. Enrichment of water bodies with nutrients (principally nitrogen and phosphorus) can result in the growth of algae and other aquatic plants that shade or clog streams. If wastewater containing biodegradable organic matter is discharged into a stream with inadequate dissolved oxygen, the water downstream of the point of discharge will become anaerobic and will be turbid and dark. Settleable solids will be deposited on the streambed, and anaerobic decomposition will occur. Over the reach of stream where the dissolved-oxygen concentration is zero, a zone of putrefaction will occur with the production of hydrogen sulfide (H2S), ammonia (NH3), and other odorous gases. Because many fish species require a minimum of 4–5 mg of dissolved oxygen per liter of water, they will be unable to survive in this portion of the stream.

Direct exposures to toxic chemicals are also a health concern for individual aquatic plants and animals. Chemicals such as pesticides are frequently transported to lakes and rivers via runoff, and they can have harmful effects on aquatic life. Toxic chemicals have been shown to reduce the growth, survival, reproductive output, and disease resistance of exposed organisms. These effects can have important consequences for the viability of aquatic populations and communities.

Wastewater discharges are most commonly controlled through effluent standards and discharge permits. Under this system, discharge permits are issued with limits on the quantity and quality of effluents. Water-quality standards are sets of qualitative and quantitative criteria designed to maintain or enhance the quality of receiving waters. Criteria can be developed and implemented to protect aquatic life against acute and chronic effects and to safeguard humans against deleterious health effects, including cancer.

Conservation and protection of environment

Conservation and protection of environment

By now, all of us have realized how important it is to protect the environment for our own survival. The term ‘conservation’ of environment relates to activities which can provide individual or commercial benefits, but at the same time, prevent excessive use leading to environmental damage. Conservation may be distinguished from preservation, which is considered to be “maintaining of nature as it is, or might have been before the intervention of either human beings or natural forces.” We know that natural resources are getting depleted and environmental problems are increasing. It is, therefore, necessary to conserve and protect our environment. Following practices help in protecting our environment.

1. Rotation of crops.

2. Judicious use of fertilisers, intensive cropping, proper drainage and irrigation.

3. Treatment of sewage, so that it does not pollute the rivers and other water bodies.

4. Composting organic solid waste for use as manure.

5. Planting trees in place of those removed for various purposes.

6. National parks and conservation forests should be established by the government.

7. Harvesting of rain water.

Some action points to protect or improve the environment:

(i) Dispose the waste after separating them into biodegradable and non-biodegradable waste material.

(ii) Start a compost heap or use a compost bin. This can be used to recycle waste food and other biodegradable materials.

(iii) Avoid unnecessary or wasteful packaging of products.

(iv) Reuse carry bags.

(v) Plant trees. They will help to absorb excess carbon dioxide.

(vi) Observe World Environment Day on 5th June.

(vii) Never put any left over chemicals, used oils down the drain, toilet or dump them on the ground or in water or burn them in the garden. If you do so, it will cause pollution.

(viii) Don’t burn any waste, especially plastics, for the smoke may contain polluting gases.

(ix) Use unleaded petrol and alternate sources of energy, and keep the engine properly tuned and serviced and the tyres inflated to the right pressure, so that vehicle runs efficiently.

(x) Avoid fast starts and sudden braking of automobiles.

(xi) Walk or cycle where it is safe to do so – walking is free; cycling can help to keep you fit.

(xii) Use public transport wherever you can, or form a car pool for everyday travel.

(xiii) Send your waste oil, old batteries and used tyres to a garage for recycling or safe disposal; all these can cause serious pollution.

Water pollution, its prevention and control:

Water pollution, its prevention and control:

Water is a key resource for our quality of life. It also provides natural habitats and eco-systems for plant and animal species. Access to clean water for drinking and sanitary purposes is a precondition for human health and well-being. Clean unpolluted water is essential for our ecosystems. Plants and animals in lakes, rivers and seas react to changes in their environment caused by changes in chemical water quality and physical disturbance of their habitat.

Water pollution is a human-induced change in the chemical, physical, biological, and radiological quality of water that is injurious to its existing, intended, or potential uses such as boating, waterskiing, swimming, the consumption of fish, and the health of aquatic organisms and ecosystems. Thus, the discharge of toxic chemicals from a pipe or the release of livestock waste into a nearby water body is considered pollution. The contamination of ground water, rivers, lakes, wetlands, estuaries, and oceans can threaten the health of humans and aquatic life.

Contaminants have a significant impact on aquatic ecosystems. for example, enrichment of water bodies with nutrients (principally nitrogen and phosphorus) can result in the growth of algae and other aquatic plants that shade or clog streams. Direct exposures to toxic chemicals such as pesticides, is also a health concern for individual aquatic plants and animals. Without healthy water for drinking, cooking, fishing, and farming, the human race would perish. Clean water is also necessary for recreational interests such as swimming, boating, and water skiing.

A. Sources of Water Pollution: Sources of water pollution are generally divided into two categories. The first is point-source pollution, in which contaminants are discharged from a discrete location. Sewage outfalls and oil spills are examples of point-source pollution. The second category is non-point-source or diffuses pollution, referring to all of the other discharges that deliver contaminants to water bodies.

Numerous manufacturing plants pour off undiluted corrosives, poisons, and other noxious byproducts to water streams. The construction industry discharges slurries of gypsum, cement, abrasives, metals, and poisonous solvents. The mining industry also presents persistent water pollution problems. In yet another instance of pollution, hot water discharged by factories and power plants causes so-called ‘thermal pollution’ by increasing water temperatures. Such increases change the level of oxygen dissolved in a body of water, thereby disrupting the water's ecological balance, killing off some plant and animal species while encouraging the overgrowth of others. Towns and municipalities are also major sources of water pollution.

In many public water systems, pollution exceeds safe levels. One reason for this is that much groundwater has been contaminated by wastes pumped underground for disposal or by seepage from surface water. When contamination reaches underground water tables, it is difficult to correct and spreads over wide areas. Discharge of untreated or only partially treated sewage into the waterways threatens the health of their own and neighboring populations as well. Along with domestic wastes, sewage carries industrial contaminants and a growing tonnage of paper and plastic refuse. Although thorough sewage treatment would destroy most disease-causing bacteria, the problem of the spread of viruses and viral illness remains. Additionally, most sewage treatment does not remove phosphorus compounds, contributed principally by detergents.

B. Dangers of Water Pollution: Virtually all water pollutants are hazardous to humans as well as lesser species; sodium is implicated in cardiovascular disease, nitrates in blood disorders. Mercury and lead can cause nervous disorders. Some contaminants are carcinogens. DDT is toxic to humans and can alter chromosomes. Along many shores, shellfish can no longer be taken because of contamination by DDT, sewage, or industrial wastes.

C. Prevention and Control of Water Pollution: Sewage should be treated before it is discharged into the river or ocean. This is possible through modern techniques.

Sewage is first passed through a grinding mechanism. This is then passed through several settling chambers and neutralized with lime. Up to this stage, the process is called primary treatment. The sewage still contains a large number of pathogenic and non-pathogenic organisms, and also sufficient quantity of organic matter. The neutralized effluents are sent to UASB (up-flow anaerobic sludge blanket). It is a reactor. In this, the anaerobic bacteria degrade the biodegradable material present in the waste water. This removes foul odor and releases methane, which can be used elsewhere. In this system, the pollution load is reduced upto 85 percent. After this, water is sent to aeration tanks where it is mixed with air and bacteria. Bacteria digest the organic waste material. This is called biological or secondary treatment. Even after the treatment, water is not yet fit for drinking. The harmful microorganisms need to be killed. The final step (tertiary treatment) is, therefore, a disinfection process, to remove final traces of organics, bacteria, dissolved inorganic solids, etc. For tertiary treatment, methods, such as chlorination, evaporation, and exchange absorption may be employed. These depend upon the required quality of the final treatment.

Apart from the above, you should also adopt the following practices:

(i) Waste food material, paper, decaying vegetables and plastics should not be thrown into open drains.

(ii) Effluents from distilleries, and solid wastes containing organic matter should be sent to biogas plants for generation of energy.

(iii) Oil slicks should be skimmed off from the surface with suction device. Sawdust may

be spread over oil slicks to absorb the oil components.