India currently generates approximately 72,368 Million Liters per Day (MLD) of sewage/ wastewater from Class I & II Citiesas per the Central Pollution Control Board (CPCB) report 2021. Out of this, 30% is treated in existing underutilized sewage treatment plants (STPs) and the rest 70% goes into surface water bodies like lakes, rivers and coasts. This reality is starkly evident in the deteriorating conditions of our rivers like Ganga, Yamuna, and other rivers in the country. The gap between sewage generation and treatment capacity is huge.
India being one of the fastest-growing countries globally, grapples with the dual challenge of rapid urbanization and declining water quality, aggravated by inadequate sewage treatment facilities. However, conventional STPs face significant challenges, including substantial land requirements, low wastewater collection, and high operation and maintenance costs, due to their energy-intensive or chemical-dependent treatment.
A CALL FOR SUSTAINABLE SOLUTIONS
India’s burgeoning population, currently surpassing 1.44 billion, and rapid urban expansion pose significant challenges to the country’s water resources management. This exerts immense pressure on both surface and groundwater sources, exacerbating the already critical situation. As a consequence, pollution levels in water bodies have skyrocketed, leading to widespread ecological degradation and posing serious threats to human health.
One of the primary contributors to water pollution in India is the discharge of untreated or inadequately treated sewage. This unchecked sewage discharge introduces a cocktail of pollutants, including pathogens, organic matter, heavy metals, and nutrients, into aquatic ecosystems. Consequently, the quality of water in these natural reservoirs deteriorates rapidly, compromising both the health of ecosystems and the safety of water supplies for human consumption and agricultural use. The contamination of water bodies disrupts fragile aquatic ecosystems, leading to decline in biodiversity and the loss of essential ecosystem services.
Conventional STPs, while essential components of urban infrastructure, often struggle to keep pace with the volume and complexity of wastewater. These treatment facilities are frequently overwhelmed by the sheer magnitude of sewage flow and the diverse array of pollutants present in wastewater. Given these challenges, there is an urgent need for alternative approaches to sewage treatment that are tailored to India’s unique socio-environmental landscape. Solutions must be sustainable, cost-effective, and scalable to accommodate the country’s growing population and urbanization trends. Embracing nature-based solutions, such as constructed wetlands (CW), hold promise as a viable strategy for mitigating the impacts of sewage pollution while promoting ecological restoration and human well-being.
CONSTRUCTED WETLANDS: A NATURE-INSPIRED SOLUTION
Constructed Wetlands (CWs) embody a nature-inspired innovation that integrates physical, biological, microbial, and engineering components to effectively treat sewage and wastewater. These systems utilize a combination of filter media, wetland plants, and microorganisms to create a microcosm of ecological balance, replicating the natural processes found in wetland ecosystems. Filter media provide a habitat for beneficial microorganisms, facilitating the breakdown of organic matter and the removal of pollutants. Wetland plants further enhance the treatment process by uptaking nutrients and providing additional surfaces for microbial colonization on their roots, thus promoting the degradation of organic matter and the uptake of nutrients.
Indigenous wetland plants within CWs have evolved to thrive in a wide range of climatic and environmental conditions, making them well-suited for sewage treatment. Their resilience to fluctuations in temperature, water quality, and nutrient availability enhances the reliability and effectiveness of CWs in various geographic regions of the world. CWs offer a cost-effective alternative to conventional sewage treatment methods, requiring minimal infrastructure and operational expenses. Once established, CWs require relatively low maintenance, further reducing the long-term operational costs associated with sewage treatment.
1. Role of Filter Media
Filter media within CWs play a crucial role in providing surfaces for microbial colonization and nutrient absorption. Filter media, for example, natural gravel, AAC (Autoclaved Aerated Concrete) blocks, activated carbon, sand, etc., within CWs act as the first line of defence, providing surfaces for microbial growth and facilitating the initial removal of pollutants from sewage and wastewater. Additionally, filter media enhance the physical filtration of suspended solids, further improving water quality.
2. Root-Microbe Interactions
Constructed Wetlands (CWs) harness root-microbe interactions to effectively treat sewage and wastewater. The dense root systems of wetland plants and the surface area provided by filter media create habitats for beneficial microorganisms, including bacteria and fungi. These microorganisms form symbiotic relationships with plant roots, forming biofilms and microbial mats. Aerobic and anaerobic processes, such as aerobic respiration and anaerobic digestion, play crucial roles in the degradation of complex organic compounds, converting them into simpler, less harmful substances.
3. Nutrient Uptake and Assimilation
Wetland plants and filter media within CWs exhibit exceptional efficiency in the uptake and assimilation of nutrients, particularly nitrogen and phosphorus, from the surrounding water. Once absorbed, nutrients are incorporated into plant biomass and microbial biomass, where they are sequestered and immobilized, effectively removing them from the aquatic environment. Indigenous wetland plants, including species such as Canna indica (Indian shot), Colocasia (elephant ear), and Cyperus alternifolius (umbrella palm), are commonly employed in CWs due to their adaptability to diverse climatic conditions and water quality parameters.
4. Oxygenation and Redox Potential
CW contributes to oxygenation and modulation of redox potential within sewage water treatment systems. Wetland plants release oxygen as a byproduct of photosynthesis, enriching the surrounding water with dissolved oxygen. This oxygenation promotes aerobic microbial activity, enhancing the efficiency of pollutant degradation processes. Additionally, the intricate root systems of wetland plants and the diverse microbial communities within filter media create microenvironments with varying redox conditions, facilitating both aerobic and anaerobic microbial metabolism.
All Images Courtesy: CSIR-NEERI
CONSTRUCTED WETLAND TECHNOLOGIES
Council of Scientific and Industrial Research (CSIR)- National Environmental Engineering Research Institute (NEERI), Nagpur, stands at the forefront of environmental science and engineering innovation in India, spearheading efforts to develop simple, safe, and cost-effective nature-based treatment solutions. CSIR-NEERI has designed, developed, and demonstrated recently patented technologies known as Up-flow Floating Surface Constructed Wetland (UFSCW) and Upflow Compact Constructed Wetland (UCCW), which are household and community-level STPs that provide efficient and affordable sewage treatment.
Upflow concept means wastewater moves from bottom to top due to the hydraulic pressure. UFSCW represents a modification of floating constructed wetlands, employing atop wastewater surfaces. This innovative system facilitates the immersion of aquatic plant roots into contaminated water, aiding in the degradation of pollutants. Through this method, oxygen is diffused by the plants, and subsequently transported via their stems to the roots. Additionally, plant roots release significant quantities of enzymes and organic acids, expediting the breakdown of large molecular pollutants in wastewater. This process enhances the bioavailability of nitrogen and phosphorus.
Another CW technology named UCCW, works on the principle of Upflow Subsurface Constructed Wetlands (USCW), which ensures maximum contact of wastewater with media and plant roots. UCCW-based STP is a type of wastewater treatment system that utilizes wetland plants and microorganisms to remove pollutants from wastewater. It is a compact decentralized treatment system that is easy to install, operate, and maintain. UCCW effectively combines anaerobic and aerobic treatment within a unified system. This integration facilitates both suspended and attached growth methodologies, thereby optimizing treatment efficiency. The system encompasses preliminary, primary, secondary, tertiary, and disinfection units within a single tank configuration, streamlining the treatment process. By consolidating these functionalities, the UCCW enhances treatment efficacy while minimizing spatial requirements, resulting in a more compact design that is both straightforward to install and operate.
Overall, the UCCW offers a sustainable and cost-effective solution for treating wastewater, while also providing habitat for ecological factors and enhancing the aesthetic value of the surrounding environment. The treated water is ready to use for irrigation, gardening, floriculture, and flushing. The UCCW-based STP demonstrates versatility in treating both sewage and grey wastewater, the latter typically containing higher organic content, particularly from kitchen sources.
CSIR-NEERI pioneered the implementation of UCCW technology, installing the first UCCW-based STP with a capacity of 1500 litres per day within the NEERI campus for sewage treatment (image above). Additionally, for greywater treatment, a UCCW-based Greywater Treatment Plant with 3000 litres per day capacity was successfully installed and showcased at the Go Vigyan Anusandhan Kendra Deolapar (image below), in Nagpur district. CSIR-NEERI is now poised to extend the reach of UCCW-based STPs, planning installations at more than 10 locations across India. This nature-based STP will vary in capacity, ranging from 5,000 to 5,00,000 litres per day, further validating the scalability and efficacy of the UCCW technology in decentralized wastewater treatment applications.
GOVERNMENT INITIATIVES ON CONSTRUCTED WETLANDS
Recognizing the importance of sustainable wastewater management and environmental conservation, the Indian government has undertaken several initiatives to promote the adoption of Constructed Wetlands (CWs) based sewage treatment plants across the country. The Central Pollution Control Board (CPCB), Ministry of Environment, Forest and Climate Change, Government of India, plays a pivotal role in formulating policies, standards, and guidelines for environmental protection and pollution control in India. Recognizing the potential of CWs in improving water quality and reducing pollution, the CPCB has issued guidelines and technical specifications for the design, construction, and operation of CW-based sewage treatment systems. These guidelines aim to standardize CW implementation practices and ensure compliance with environmental regulations. The government supports research and development initiatives focused on advancing CW technology and optimizing its performance for diverse environmental conditions in India. These initiatives contribute to the continuous improvement and refinement of CW-based sewage treatment systems in the country. Through these initiatives, the Indian government is actively promoting the adoption of Constructed Wetlands as a sustainable and nature-based solution for sewage treatment, contributing to the nation’s efforts towards water security, environmental sustainability, and public health improvement.
CHALLENGES AND FUTURE PROSPECTS
The widespread adoption of Constructed Wetlands in India holds immense promise for mitigating water pollution issues. However, several challenges must be addressed to realize their full potential and ensure their effective implementation across diverse environmental contexts. Public awareness and acceptance of Constructed Wetlands may vary depending on cultural attitudes, socio-economic factors, and community engagement efforts. Building public awareness through education, outreach, and participatory decision-making processes can enhance community support and acceptance of CW projects, fostering long-term sustainability and success. Future research endeavours should focus on advancing CWs design, performance, and scalability to meet evolving sewage treatment needs. Moving forward, concerted efforts from all stakeholders are essential to overcome these challenges and unlock the full potential of CWs in India’s efforts to achieve sustainable water management and environmental conservation.
ENVIRONMENTAL AND SOCIOECONOMIC BENEFITS
By harnessing the inherent capabilities of filter media and wetland plants within CWs, India can address its sewage treatment challenges in a sustainable and environmentally responsible manner. Moreover, the widespread adoption of CWs holds the potential to not only improve water quality but also enhance ecosystem resilience and promote biodiversity conservation across the country’s diverse wetland habitats. Further, CWs create opportunities for decentralized wastewater management, empowering local communities and fostering green entrepreneurship in sectors like floriculture, aquaculture, and biofuel production.
*The writer is Senior Principal Scientist & Incharge, Wastewater Management Sub-Vertical, CSIR-NEERI (National Environmental Engineering Research Institute), Nagpur.
