Abstract
Vegetation filter is an emerging wastewater treatment option in which phytoremediation strategies are employed for municipal applications. Short rotation woody crops combine both treatment and reuse of effluent and operate on ‘zero discharge' concept. This multifunctional system has become a viable alternative solution for wastewater treatment as well as biomass production by utilizing nutrient rich wastewater as cost efficient fertilizer. Fast growing species like Salix, Eucalyptus, and Populus with high water and nutrient requirements, highly selective heavy metal uptake and high evapotranspiration rate are generally preferred as vegetation filters for wastewater treatment. However, site-specific factors such as wastewater composition, climate, soil type, permeability, species or clonal characteristics must be taken into account when considering irrigation with municipal wastewater. This chapter discussses the prospects for vegetation filters to remediate contaminated water and soil and also facilitate recycling of valuable resources in society.
TopIntroduction
Water quality management is a vital task for all countries. Wastewater can seriously deteriorate the quality of their receiving water bodies. As the freshwater sources are either becoming scarcer or polluted through human intervention, the wastewater reuse is becoming an important issue in the world with increasing demand for water for human consumption, agriculture and industrial purposes. The volume of wastewater generated will be increased in the future with increase in consumption and the treatment capacity will also be increased to keep pace with it. Table 1 shows the inconsistent water supply, wastewater generation and treatment scenario in India (Central Pollution Control Board [CPCB], 2009). Around 38,250 MLD of wastewater is generated by class I and class II cities in India (but, the installed sewage treatment capacity is merely 11786 MLD) which is estimated to grow 3.5 times to about 132 billion litres per day of wastewaters (with a potential to meet 4.5% of the total irrigation water demand) by year 2050 (Bhardwaj, 2005). Thus, it indicates that in coming years, there will be a twin edged problem to deal with reduced fresh water availability and increased wastewater generation due to increased population and industrialization.
Table 1. Trends of water supply, wastewater generation and treatment facility available in Class-I and Class-II cities of India (Source: CPCB, 2009)
| Year | Water Supply
(MLD) | Sewage Generation
(MLD) | Treatment
(MLD) |
| Class-I | Class-II | Class-I | Class-II | Class-I | Class-II |
| 1978-79 | 8638 | 1533 | 7007 | 1226 | 2756 | 67 |
| 1989-90 | 15191 | 1622 | 12145 | 1280 | 2485 | 27 |
| 1994-95 | 20607 | 1936 | 16662 | 1650 | 4037 | 62 |
| 2003-04 | 29782 | 3035 | 23826 | 2428 | 6955 | 89 |
| 2008-09 | 44769 | 3324 | 35558 | 2696 | 11553 | 233 |
Key Terms in this Chapter
Land Treatment System (LTS): Land treatment refers to the application of partially treated wastewater to the land that is designed, constructed and operated to treat wastewater through the use of crops, irrigation methods, ground and surface water monitoring to confirm to specific water quality limits. It involves the controlled application of wastewater to the land at rates compatible with the natural physical, chemical and biological processes that occur on and in the soil.
Treatment Efficiency: The treatment efficiency of any natural treatment system is the basic indicator of its phytoremediation potential. It depends on the amount and composition of wastewater, type of plant species used, climatic and other conditions.
Short Rotation Woody Crops (SRWC): “Short Rotation Crops” means woody crops such as willows, poplars, Robinia and Eucalyptus with coppicing abilities as well as lignocellulosic crops such as reed canary grass, Miscanthus and switch grass.
Nutrients: Nutrients are the nutritious components in foods that an organism utilizes to survive and grow. It refers to mainly nitrogen and phosphorus originating from agricultural and urban areas.
Biomass: Biomass is biological material derived from living, or recently living organisms. It most often refers to plants or plant-based materials which are specifically called lignocellulosic biomass. As an energy source, biomass can either be used directly via combustion to produce heat, or indirectly after converting it to various forms of bio fuel.
Vegetation Filters: Vegetation filter is a plant-based natural treatment system which principally involves phytoremediation strategies for treatment of wastewater through fast-growing woody ( e.g . Salix , Populus ) trees and/or herbaceous perennials ( e.g . Phragmites australis ). In a properly designed VFS, water flows evenly through the strip, slowing the runoff velocity and allowing contaminants to settle from the water.