Silt Recycling Companies - Research Paper Example

? Topic: Silt recycling Companies Lecturer presentation Introduction Silt is an important component produced in many natural and artificial processes. According to Yabuki (2006: 51), agricultural and industrial processes produce vast volumes of silt annually. A study conducted in United Kingdom, established that five soil-washing plants produced about 1000 tonnes of silt per day (Calabrese, et al. 2005). The composition and the quality of silt differ, but high concentration of diverse minerals and large volumes of silt have jolted many companies into recycling the sediments. Volkmar, et al, (2005:43) noted that silt is formed from various weathering processes that result to the breakdown of weakened sand quartz crystals structures. In addition, sludge consists of substantial amounts of silt. There are various weathering processes involved in the breakdown of these crystals including chemical, biological and physical weathering processes. However, physical weathering is the most prevalent method of silt formation that occurs in artificial processes such as building, transport, grinding and construction, (Volkmar, et al, 2005: 59). Similarly, substantial amount of silt is formed from glacial movements and in deserts or semi arid regions (Agathos and Walter, 2005: 28). Importance of silt recycling Silt recycling is an important economic and environmental practice and many companies are currently engaged in the business. Silt is normally transported and deposited in water bodies such as lakes, dams, and rivers. According to Balata, Piazzi, and Benedetti (2007:79), soil erosion especially in rural areas and construction industry in urban areas causes massive transportation of silt into water bodies. When the sediments are retained in the water bodies, they reduce the volume of water that could be stored in the water body and this causes diverse environmental, social, and economic problems. These include reduced capacity of producing hydroelectric power, flooding and lack of enough water to sustain the surrounding communities (Benbi, and Nieder, 2008: 43). In pastoral communities especially in dry areas, De’ Haas, et al (2005) noted that siltation in dams is one of the major cause of conflict. In addition, siltation in dams increases the cost of maintenance and water treatment. Consequently, water supply, fisheries and tourism are adversely affected. Moreover, silt deposits forms one of the most fertile regions for crop cultivation and some regions along major rivers such as river Nile and Mississippi are some of most important food producing parts in the world (Cerling, James, and Denise (2005). In this respect, silt recycling is important in order to enhance its economic importance and minimize the adverse environmental impacts. Many companies are currently engaged in silt recycling business because of environmental and economic reasons. Silt recycling provides an effective way of improving the health of agricultural soils and at the same time enhancing the capacity of water storage bodies. According to Benbi and Nieder, (2008: 38), the interactions between lands, water and human beings are highest in water bodies such as dams and the resulting sediments provides very high agricultural and ecological potentials. Because of the discovered potential, companies are increasingly recycling silt to improve agricultural capacity of soils, while at the same time enhancing the capacity of the water bodies to store water and serve their ecological and environmental functions. In addition, silt recycling provides companies with the opportunity of reducing the environmental impact of the silt especially in regions where the soils has been contaminated by harmful chemicals and heavy metals (Sutherland, and Meyer, 2007: 91). In construction industry, silt is produced in large quantities and it presents serious storage and transportation problem. In such circumstances, silt-recycling companies in the construction industry make sand and coarse aggregates from silts and fines that are used in other construction processes. According to Rahel and Olden (2008), processing the silt into course aggregates minimizes the need for other aggregates and preserves landfill space. Companies engaged in silt recycling in Europe Several companies are engaged in doing the same kind of silt recycling work in the United Kingdom and Europe. They include Suez Environment and DEME environmental contractors. Suez environment is based in France and it specializes in water treatment and waste management activities. The company has many subsidiaries in different parts of the world and their main objective is the protection of natural resources and ecosystems. The key areas of the company’s operations include water and waste sectors. In the water sector, the company deals in conservation of the catchment areas in addition to treating and distributing water. Moreover, Suez environment deals in collecting and purifying industrial and domestic water. Other operations of the company in the water sector include biological production of energy from waste products emanating from the water purification process. In the waste sector, Suez Environment deals in collection of all kinds of waste materials with exception of radioactive substances (Suez Environment, 2006). The wastes are selected and then subjected to preliminary treatment and then recycled to various products. The company operates under strict environmental regulatory mechanisms to ensure that the clients benefit economically and ecological balance is preserved (Suez Environment, 2010). Suez Environment operates about 145 hazardous waste management programs worldwide, ranging from transit consolidation to pre-processing in addition to super efficient treatment and recovery operations. Silt recycling operations in the company entails removal of soil pollutants and other particulate industrial effluents (Suez Environment, 2010). According to Dorlands et al (2006: 72), organic substances and minerals are the major causes of soil pollution. The company undertakes the diagnosis and audit on the contaminants on the affected region followed by the most appropriate treatment. Suez environment employs over 80,000 people globally and in 2005, the company had a gross turnover of 12 billion Euros. During the same period, the company recovered 817,000 tonnes of waste silt from cement plants. Moreover, Suez environment produced 218, 178 MW of thermal energy from treatment of the waste (Suez Environment 2006). DEME Environmental Contractors (DEC) is another silt recycling company in Europe with branches in different countries around the world. DEC is an international conglomerate based in Belgium. It specializes in groundwater and soil remediation, treating sediments, recycling and landfill techniques in addition to environmental dredging. DEC has undertaken many silt and sediment treatment projects in different pats of the world including redevelopment of brown fields, sediment and sludge treatment and many multidisciplinary projects. In Belgium, DEC owns several sediments and soil recycling plants in Antwerp, Ghent and Zeebruge. The company falls under Ecoterres Holdings, which consolidates all environmental companies in DEME group. The Ecoterres group employs about 522 employees and in 2009, it had a turnover of 150 million Euros (DEC 2010). Techniques for recycling sludge Sludge recycling plants normally use three techniques for recycling. The methods include agricultural recycling, land filling and incineration (Cassidy, 1998: 34). Agricultural recycling aims at recovering essential plant nutrients mainly phosphorous, nitrogen and carbon. These nutrients can be concentrated to form ‘bio soils’ that can be used directly in farms or concentrates in fertilizers. Land filling takes place in landfills, where municipal waste is mixed with the sludge. In the landfill, the mixture is subjected to anaerobic decomposition producing bio fuel that is converted to heat or electrical energy. Incineration is the other technique applied for recycling sludge. This method destroys organic matter because it entails thermal oxidation. However, it recovers mineral and elemental byproducts from the sludge (Cassidy, 1998: 69). Incineration in conjunction with wet air oxidation is used to recycle hazardous wastes and byproducts from building and construction such as concrete. The recovered materials from the process are used in construction and metal industries. In addition, incineration generates energy in form of heat or electricity. Most recycling plants apply all of the above methods to recover useful products from sludge and reduce the volume of the wastes. KREPRO is an example of sludge and wastewater-recycling process (Cassidy, 1998:73). According to Karlsson (2001:31), KREPRO process recovers bio fuel, metals, ferric phosphorous and carbon from sludge. The first stage in KREPRO process entails acidifying thickened sludge with sulfuric acid to dissolve most of the inorganic salts. The acidified sludge is then hydrolyzed thermally, dissolving most organic matter. This stage separates inorganic particulate matter such as sand and heavy biodegradable organic material, because they are not soluble. After the separation, the sludge that now contains dissolved metals and phosphorous is cooled. Ferric salts and alkali are added to the solution and phosphorous is precipitated as ferric phosphate (Cassidy, 1998:82) The ferric phosphate compound is separated using centrifuge. The isolated biodegradable organic materials are incinerated to produce energy in form of heat or electricity. After incineration of biodegradable materials, heavy metals form a significant proportion of the residue and they are separated. Finally, the separated products are refined for application in diverse areas. Ferric phosphate is used as a fertilizer while heavy metals are recycled and sold to industries that use them (Cassidy, 1998:86). Ecological and environmental impacts of silt recycling plants The construction of a silt recycling plant has profound ecological impacts. Most industrial and agricultural silts are carried into water bodies where they settle down, causing pollution. Recycling and removal of silt and sediments in aquatic ecosystem eliminates some of their adverse effects. According to Rehg, Packman, and Ren (2005), excessive accumulation of silt in water bodies is one of the most challenging forms of pollution in aquatic environments. Though natural processes contribute to substantial amounts of sediments, human activities have accelerated siltation in water bodies five to ten times more. The sediments affect a wide range of human of activities, but biological production, diversity and ecological balance in water are the worst affected (Rehg, Packman, and Ren, 2005). According to Heywood and Walling (2007:1082), soil erosion is one of the major causes of offsite siltation and sedimentation in water bodies. Rahel and Olden (2008: 591) estimated that about 2.3 billion tonnes of sediments deposited in rivers originate from human induced soil erosion. From these sediments, about 1.9 tonnes are deposited in water reservoirs, lakes, flood plains and rivers while the remainder reaches the coastal waters. Other notable human induced factors of sedimentation in water bodies include building and construction industry, mining, urban development among other factors. According to Pimentel (2006: 1305), extreme deposition of sediments is one of the key forms of anthropogenic disruption of aquatic ecosystems in temperate and tropical regions. The first immediate effect of silt is disruption of physical and chemical processes in the aquatic environment (Olden, J, et al 2005: 1273). Reduction in the quantity of light that penetrates through the water is one of the most profound physical effects of sediment accumulation in aquatic ecosystems. The suspended particles absorb and scatter light energy reducing the compensation depth, which is the maximum distance that light energy can initiate photosynthesis in aquatic plants. The immediate effect is reduction in food production by the primary producers in the water (Okun, Lewin, and Mehner, 2005). A study conducted by Lehtiniemi, Engstrom, and Viitasalo (2005: 1083) in Alaska established a drastic drop in compensation depth following an increase in water turbidity that was caused by silt. An increase of 2-10 Nephelometric Turbidity Units (NTU) reduced primary production of the lake by about 75%. Moreover, minerals in silt increases water turbidity further, leading to obstruction of blue light that provides energy for photosynthesis to take place. Besides tampering with primary food production in aquatic ecosystems, limited light penetration affects behavior response of aquatic life resulting to further ecological imbalance in water (Lehtiniemi, Engstrom, and Viitasalo 2005). Accumulation of sediments in water causes oxygen reduction in the aquatic environment. Jeppesen, et al (2005:1750) noted that sediments have the ability of deoxygenating up to sixteen times of their volume in well-aerated water. Reducing the amount of oxygen concentration available disrupts the gaseous exchange processes of the marine life leading to suffocation. Silts and sediments contribute to changes in the temperature of water. Particles that absorb heat from the surrounding increases the temperature of water and others causes a decrease in the temperature due to reflection of heat. The changes in temperature destabilize the physiological and reproductive functioning of the aquatic organism (Jeppesen, et al, 2005:1750). Increased sedimentation blocks crevices in the rocks that make the seabeds and this prevents oxygen penetration and exchanges in the aquatic ecosystem (Jeppesen, et al, 2005:1759). Consequently, the biogeochemical and microbial processes become disrupted remarkably. Concentration of nutrients, pesticides, trace element and heavy metals in water bodies is another important environmental effect of silts. Excessive accumulation of nutrients such as phosphorous promotes rapid growth of water plants, which disrupts gaseous exchange, and penetration of light in the water. In addition, the accumulated toxic elements are incorporated in the food webs increasing toxicity levels in aquatic animals (Huber, Adrian and Gerten, 2008:805). Interactions between chemical elements contained in the silt and water chemistry determine whether the resulting composition becomes a source or sink of nutrients or source of contamination. In this respect, chemical and physical interaction of sediments plays a crucial role in determining the ecological environment of aquatic life. Environmental benefits of sludge recycling Construction of silt recycling plant would help in mitigating the effects of sludge to the environment in several ways. Converting sludge into useful products reduces the volumes carried into water bodies. Silt from building and construction activities is processed and separated into various components. The finer silt mixed with cement binders and polymer additives form aggregate materials (Heywood and Walling 2007: 981). A study conducted by De’ Haas et al (2005:19-29), established that sediments in water reservoirs contain large quantities of essential plant nutrients, such as carbon, nitrogen and phosphorous. These recycled sediments are used for enriching agricultural farms in different countries. Silt recycling companies have put sustainable environmental efforts to remove toxic chemical elements in soils. These include wastewater management, detoxifying wastes and enforcing environmentally friendly practices (Agathos and Walter 2005: 69). This ensures that the ecological integrity of water is preserved. Excavating the accumulated sediments in water reservoirs helps in restoring the maximum water holding capacities for dams. In addition, removing the silt enhances penetration of light in deep water horizons and consequently, algae and other primary producers can photosynthesize food for organisms in the higher trophic levels in the aquatic ecosystem (Calabrese, et al 2005). Recycling sediments reduces emissions of greenhouse gases by minimizing the energy that would have been needed to manufacture new products such as fertilizers for agricultural use. Sludge recycling processes emit energy from the decomposition of the organic matter, including biogas. The energy produced in the process is beneficial to the environment because it reduces the consumption of fossil fuels that contribute vast volumes of greenhouse gases. Moreover, restoring the aquatic ecosystems by recycling sediments helps in increasing the productivity and diversity of marine life (Cerling, James and Denise 2005: 36). Sludge and dumpsites pollute air by emitting unpleasant odors from decomposing organic matter. When sewerage and other organic domestic wastes are not recycled, they provide favorable grounds for breeding of disease causing microorganisms. These pathogens are normally carried by vectors such houseflies and rats resulting to health problems. In this respect, recycling the waste cleans the environment from the potential health hazards. Industrial and economic benefits of sludge recycling Silt recycling offers industrial plants with several benefits. The process is a cost effective method of disposing waste products originating from processing and manufacturing processes. Industries produce vast amounts of waste products including silt that require large spaces and expensive methods of disposal (Seckbach, 2007: 67). Recycling silt adds value to the waste product and this minimizes the cost of disposal. In addition, the industries generate additional revenue by selling the recycled products. Silt recycling generates additional energy that is applied in other processes within the industry (Seckbach, 2007: 82). This helps in minimizing the operational costs of the industries. Sludge recycling benefits agricultural industries by generating cheaper alternatives of increasing soil fertility. Recycling helps in promoting better agricultural practices such as controlling soil erosion. In this respect, it enhances the production capacity of agricultural regions further. Accumulation of silt in water reservoirs for producing hydroelectric power reduce their ability to operate at optimum capacities. Recycling the sediments restores the water capacity that enhances the hydroelectric potential of the power plants. Equally important, economic activities such as fishing benefit immensely from silt recycling. Removing the sediments improves the breeding environment of aquatic organisms in addition to minimizing the accumulation of toxic elements along the food webs. Other economic benefits of silt recycling are creation of job opportunities in the industry and promoting the growth of other sectors such as tourism (Dorlands, et al 2006: 102). Conclusion The amount of sludge produced worldwide is increasing at an alarming rate mainly because of raising global population. The population has exerted enormous pressure on the available natural resources leading to adverse environmental effects such soil erosion. In addition, human activities including building and construction industry have increased to create the necessary infrastructure for the population (Dembski, et al 2008:40).These factors generate large volumes of silt that is eventually deposited in water reservoirs. The sediments cause heavy economic, social and environmental damage. Some of the adverse effects include loss of water storage capacity in dams, reduced power production in hydroelectric dams, and pollution of aquatic environment. These effects affect other industries including agriculture, fishing, manufacturing and processing in addition to tourism. Constructing silt-recycling plants offer attractive economic and environmental benefits to many sectors. In the agricultural sector, recycling helps in prevention of soil erosion and processed silt improves soil fertility. In the fishing industry, silt recycling reduces the level of pollution and toxicity caused by accumulation of sediments. This promotes aquatic production and diversity that not only enhances fishing industry, but others like tourism. In the industrial sector, silt recycling helps in producing clean source of energy in hydroelectric plants that reduces emission of greenhouse gases. Moreover, silt recycling creates direct and indirect employment opportunities. References Agathos, N. and Walter, R. 2005. Biotechnology for the environment: Soil Remediation. NJ: Kluwer Academic Publishers. Balata, D., Piazzi, L. & Benedetti, L. (2007). 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