International Journal of Advance Engineering and Research Development ROOT ZONE METHOD FOR TREATMENT OF WASTE WATER

Transcription

1 Scientific Journal of Impact Factor (SJIF): 4.72 International Journal of Advance Engineering and Research Development Volume 4, Issue 2, February e-issn (O): p-issn (P): ROOT ZONE METHOD FOR TREATMENT OF WASTE WATER Urvij Dave 1, Garima Patel 2, Chintan Patel 3, Tejasvi Patel 4 and Hardik Patel 5 1,2,3,4,5 Department of Environmental Science and Technology, Sroff S.R. Rottary Institute of Chemical Technology, Abstract : Applied research has demonstrated that selected plant species possess the genetic potential to remove, degrade, immobilize, or metabolize a various types of contaminants. More than 400 plant species have been identified by the scientists who can remediate water from which we have selected the most major and easily available plants in India. These plants are planted in the zone like that, it remains in contact with the effluent. Other component like microorganisms would develop naturally on the roots of the plants which will treat the effluent as a food. Its limitation lies within the very biological nature of this unique approach. A pilot wetland system consists of a sedimentation tank with a coarse-grained solids filter, an exposed basin with drainage of PVC pipes, and an inspection well at the basin outlet. The basin is filled with layers of gravel and sand, planted with aquatic plants and have approximately 30 0 slopes is kept for the flow of the effluent and having perforated long inlet pipe for. The filter bed is consist by three layers, the bottom layer filled with coarse sand (10cm), the intermediate layer filled with fine-grained gravel (10 cm), and the top layer filled with sand (10cm) and a space of 10 cm be left for efficient plant growth. Root zoning method is successful for the sewage waste water treatment in many parts of the world. Thus, the objective of this review paper is to provide a method that is accessible to those who need to evaluate alternate cost effective remedial technologies for the industrial waste water treatment. Index Terms Aquatic Plants, Constructed Treatment Wetland (CTWs), Root Zone System 1. INTRODUCTION 1 The treatment of Waste Water is done by physical, chemical and biological processes. Microbial organisms supports these processes. Conventional treatment system, therefore, contribute to: i) Depletion of non-renewable sources, and ii) Environmental degradation that occur due to extraction of non-renewable resources, and also due to the by-products / final products of these technologies, such as bio-solids and sludge. Therefore, attempts for developing cost-effective treatment approach are always surrounded by using only the natural components and free from any mechanical requirements that needs energy. Plants which purify the wastewater has always attracted researcher and holds directly to the general public as wall. Therefore, many natural systems such as oxidation ponds / lagoons, land application systems, etc. use the ability of plant species in retorting or lowering the pollutants where developed. Constructed wetland systems now-a-days have emerged as an attractive low-cost wastewater treatment alternative. Constructed treatment wetlands appear to be a suitable alternative both in developed and developing countries for natural treatment systems. Constructed wetland treatment systems have been in operation in many of the European and American countries. Significant advances have been made in the engineering knowledge of creating constructed wetlands. There is growing interest also in India to develop and adopt the technology for water pollution control to suit the local conditions. 2. TYPES OF CONSTRUCTED TREATMENT WETLANDS (CTWS) Depending on the level of water column, constructed treatment wetlands for wastewater can be classified into two categories: 1. Surface flow (SF) wetlands, and 2. Sub- surface flow (SSF) wetlands. In surface flow wetlands the substrate bed is densely vegetated and there will be a water column above the surface of the bed as shown in Fig 1. All rights Reserved 418

2 Fig 1: Surface wetland construction The SF systems are flooded and expose water surface in the system to the atmosphere. Plants predominantly grow on soil bed in these systems and the depth of water column is typically less than 0.4m. In sub- surface flow wetland, the water level is maintained below the surface of the substrate bed as shown in Fig 2. Fig 2: Subsurface wetland construction The substrate medium in SSF wetlands is usually made of gravel to provide high void space to enable wastewater loaded on the bed to quickly seep through the bed. Soil based SSF wetlands also are found in northern Europe. Depending on the direction of flow of applied wastewater, SSF wetlands can be either horizontal flow type or vertical flow type. In horizontal SSF systems, the medium is maintained water saturated through continuous application of wastewater. The bed depth of horizontal SSF wetlands is typically less than 0.6m and the bottom of the bed is sloped to minimize flow above the surface. In vertical SSF wetlands, wastewater is applied through different arrangement of wastewater feeding and collection mechanisms to maintain a vertical direction of flow. This is achieved either by intermittent wastewater application or by burying inlet pipes into the bed at a depth of cm. The total depth of bed is in the range of 2-3m. Since the wastewater infiltrates through the substrate bed this type of wetlands are also called infiltration wetlands. Constructed wetlands are also classified on the basis of how macrophytes grow in the system. Thus, CTWs can be; 1. Floating macrophye systems; 2. Submerged macrophyte systems; 3. Rooted emergent macrophyte systems. Floating macrophytes are plant species that float on the surface of the water and do not require a substrate for their growth. Algae, duckweed, water hyacinth are some of the floating macrophytes adopted for wastewater All rights Reserved 419

3 Submerged macrophyte systems have plants species that are submerged in the water column and do protrude beyond the water surface. Rooted emergent macrophytes are plants that are generally attached to the substrate in the wetland with leaves extending above the water surface. Unless specifically mentioned otherwise, wetland treatment systems commonly mean constructed wetlands planted with rooted emergent macrophyte species. Root zoning method can be defined as the efficient use of plants to remove, detoxify or immobilize environmental contaminants in a growth matrix (soil, water or sediments) through the natural biological, chemical or physical activities and processes of the plants. Plants are unique organisms equipped with remarkable metabolic and absorption capabilities, as well as transport systems that can take up nutrients or contaminants selectively from the growth matrix, soil or water. There are several ways in which plants are used to clean up, or remediate, contaminated sites. To remove pollutants from soil, sediment and/or water, plants can break down, or degrade organic pollutants or contain and stabilize metal contaminants by acting as filters or traps. It is an alternative or complimentary technology that can be used along with or, in some cases in place of mechanical conventional clean-up technologies that often require high capital inputs and are labour and energy intensive. 3. POLLUTANT REMOVAL MECHANISM Removal of pollutants in a constructed wetland is believed to be accomplished in the following ways: Direct uptake of pollutants by plants Plants providing large surface area on which microbial degradation occurs Decreasing flow velocities which increase residence time and allow to sediment the solids and removal of pathogens by the excretion of antibiotics by plants Plant s root provide filtration of large particle Adsorption of nutrients by substrate media There are three main removal processes for the removal of pollutants is: i. Physical processes The presence of plant biomass and substrate media will physically provide the retard in the pathways of wastewater enhancing the sedimentation of suspended solids. And the media acts as filter a filter bed as in filtration processes. Thus plants and media remove the pollutants by physical process. ii. Chemical processes iii. Chemical reactions occurring between the substances, especially metals,forms their precipitation as insoluble compounds in the water. The breakdown of organic pesticides and destruction of pathogens can be occurring in the exposure of the sunlight and atmospheric gases. Biological processes: Biological processes play an important role in the removal of pollutants. There are six major biological reactions that have been identified for the removal of the pollutants are: i) Photosynthesis: The removal of organic carbon from waste water column and addition of oxygen is resulted by the photosynthesis process done by the wetland plants. ii) Respiration: The oxygen released by the hairs of the plant s root will provide the water rich of oxygen and this presence of oxygen will provide partial aerobic condition. iii) Fermentation: In the absence of oxygen the decomposition of organic carbon will provide the energy-rich compounds like alcohol, methane and volatile fatty acids. iv) Nitrification: Oxygen with carbon, organic pollutants or biological degradation drives the nitrification All rights Reserved 420

4 v) Denitrification: The removal of the nitrogen by the micro-organisms is done in this process. vi) Microbiological phosphorus removal A layer of bio-films will be developed on the micro-organisms and substrate present in sediments and removal of microbiological phosphorus will occur. 4. ADVANTAGES It achieves standards for tertiary treatment with low cost, such as no electricity, no chemicals for ph adjustment. Low maintenance cost, since it involves no machinery and its maintenance. It requires negligible attendance for operation and monitoring. It has no sludge handling problem. It enhances the landscape and gives the site a green appeal. It provides natural habitat for birds and after few years gives an appearance of bird sanctuary and also provides recreational and educational areas. Though it is a sewage treatment plant it doesn t have odor problems. It becomes a green Zone and it does not have mosquito problem. Above all it provides eco friendly solution to waste water treatment naturally. The reeds are not grazed by ruminants. Salinity may not be a problem for a survival or operations of reed beds. It is recommended to combine vertical flow and then horizontal flow of sewage with a soil having impervious bottom. 5. LIMITATIONS They require large land area for the same level of treatment by conventional systems for large cites. Require long period, typically two or three growing seasons for the vegetation for optimal treatment efficiencies to be achieved. The process dynamics of the CTW systems are yet to be fully understood leading to estimated design and operating criteria. These system typically lie outdoor and spread over large area Their performance is mark to storm, wind, and floods. 6. SPECIES OF PLANTS USED IN ROOT ZONING METHOD In the natural setting, certain plants have been identified which have the potential to uptake heavy metals. At least 45 families have been identified to hyper accumulate heavy metal; some of the families are Brassicaceae [2], Fabaceae [2], Euphorbiaceae [2], Asteraceae [2], Lamiaceae [2] and Scrophulariaceae [2]. Brassica juncea, commonly called Indian mustard, has been found to have a good ability to transport lead from the roots to the shoots. Indian mustard (B. Juncea) is a high biomass, rapidly growing plant that has an ability to accumulate Ni and Cd in its shoots. It is a promising plant for phytoremediation. Aquatic plants such as the floating Eichhornia crassipes (water hyacinth), Lemna minor (duckweed), and Pistia have been investigated for use in rhizofiltration [2]. Recently, a fern Pteris vitatta has been shown to accumulate as much as 14,500 mg kg 1 arsenic in fronds without showing symptoms of toxicity. Corn, sunflower and sorghum were found to be effective due to their fast growth rate and large amount of biomass. Gardea-Torresdey et al. (2000) have shown that Alfalfa is a potential source of biomaterials for the removal and recovery of heavy metal ions. Some species of plant species are used in the biological treatment of the wastewater. Four species are considered suitable, Eichhornia crassipes (water hyacinth), Alternanthera philoxeroides, Justicia americana and Typha latifolia are efficiently remove phosphorous from effluent [2]. Water hyacinth was grown in the laboratory in culture solutions containing phosphorus at varying concentrations. The Phosphorous concentration critical for maximum growth was 0.1 ppm. Below this level growth was limited; above it the hyacinths took up Phosphororus in luxury amounts without any increase in yield. Water hyacinth was grown outdoors in concrete tanks containing sewage effluent. Over a period of five weeks the uptake of P was measured as 5.5 mg/g of the dry weight of the plant. The P concentration in the effluent was 1.4 mg/ liter at the start of the experiment and was reduced to 0.2 mg/litre at the end. Of this decrease 70% took place in the first two weeks All rights Reserved 421

5 80% by the end of three weeks. The hyacinth increase in (dry) weight was at a maximum during the first week and totalled 97 g/m2 of water surface, which represented a 45% increase in the dry weight of the plants at the start of the experiment. Typically, plant species grow autographically, i.e. they use sunlight as the energy source and inorganic carbon (CO2) along with inorganic nutrients (N, P, etc.) to form biochemical energy through photosynthesis. In wastewater treatment, autotrophic metabolism is the most reported way for inorganic pollutants uptake and removal. As illustrated plant species can remove inorganic N and P from primary effluent, secondary effluent, or centrate from sludge digestion. Aquatic plant species and their uptake (kg/ha/year) Element E. crassipes J. americana J. americana T. latifolia N P S Ca Mg K Fe Cu Table 1: Uptake of various elements by selected aquatic plants [2] 6.1. Equations The simplest of the model for treatment of domestic wastewater is adopted in UK, where treatment wetland is mostly deigned as subsurface flow systems. For horizontal system, the surface area A h is calculated using following model (copper and green 1998). (1) Where, = average daily flow rate of wastewater, m3/day = average BOD of the influent, mg/l = average design BOD of the effluent, mg/l = reaction rate constant, m/day Pollutant removal in treatment wetland thus, can be expressed as follows: (2) Where, = average design BOD of the effluent, mg/l = average BOD of the influent, mg/l t= hydraulic retention time, day = temperature dependent first order reaction rate constant, All rights Reserved 422

6 .(3) Where, L = length of wetland, metre W = width of the wetland, metre D = depth of water column, metre n= porosity of the substrate medium, Q = average flow rate, m3/day Rearranging the terms to obtain the area of subsurface flow wetland required, = LW =..(5) The value of the rate constant is estimated using the following equation: =....(6) Where is the temperature coefficient for rate constant. The value of and depend on the type of pollutants encountered in surface and subsurface flow systems. Value for common pollutants are presented in table 2: Pollutant Surface flow systems Subsurface flow systems BOD Nitrification Denitrification Pathogen Removal Table 2: Temperature coefficients and rate constant 7. REFRENCES [1] Phytoremediation of heavy metals: Recent techniques, African Journal of Biotechnology, Vol. 8 (6), pp , 20 March, 2009, ISSN , 2009 Academic Journals [2] Process and Plants for Wastewater Remediation, a review, International Journal of Environment and Bioenergy, 2012, 2(3): [3] Wastewater Management By Rootzone Technology, International Journal of Computer & Organization Trends Volume 2 Issue 2 Number 2 Apr 2012 [4] Root Zone Technology: Reviewing its Past and Present, International Journal of Current Microbiology and Applied Science [5] Phytoremediation of Industrial Wastewater Potentiality By Typha Domingensis, Int. J. Environ. Sci. Tech., 8 (3), , Summer All rights Reserved 423

7 [6] Root Zone Technology For Campus Waste Water Treatment, Journal of Environmental Research And Development Vol. 3 No. 3, January-March 2009 [7] Wastewater Treatment through Root Zone Technology with Special Reference to Shahpura Lake of Bhopal (M. P.), India, International Journal of Applied Science and Engineering, , 3: [8] Wastewater purification plant by means of plants, US 7, 718,062 B2. [9] Introduction to phytoremediation, national risk management research laboratory office of research and development, u.s. environmental protection agency [10] Constructed wetlands for waste water treatment, All rights Reserved 424