Water shortage is becoming a serious problem due to the growing population and urbanisation in the country. The depletion of clean water resources is continuously widening the demand-supply gap. To bridge this gap, other sources of water supply need to be explored. Reuse and recycling of wastewater could be considered, given the emergence of treatment technologies. Wastewater treatment is a multi-stage process of recycling wastewater for reuse. The aim is to reduce or remove organic matter, solids, nutrients and disease-related organisms to make the water fit for use.
The reuse of wastewater is crucial to reduce the ever-increasing gap between fresh water supply and demand in urban areas. Besides, it is important to offset the cost of water delivery to mitigate resource allocation conflicts across sectors and regions, increase water use efficiency and reduce groundwater extraction, and make the water and sanitation sector sustainable.
Water recycling technologies
There are a number of technologies available for wastewater treatment. While choosing from the various options available, the focus should be on water quality, value, and sustainable design and engineering. Some of the technologies available are:
- Activated sludge process (ASP): It is a process of treating sewage and wastewater using bacteria (to degrade the biodegradable organics) and air. There are many variants of ASP subject to variations in the aeration method and the way sludge is returned. ASP offers efficient removal of biochemical oxygen demand (BOD), chemical oxygen demand and nutrients.
- Wastewater stabilisation ponds: These are also called oxidation ponds. They act as holding basins for secondary wastewater treatment. The organic matter is decomposed naturally. The waste is stabilised and pathogens are reduced through the action of bacteria and algae.
- Submerged aerated fixed films technology: This process is used to reduce the organic loading of residential and commercial sewage and wastewater. It reduces BOD and a significant quantity of suspended solids. It also significantly improves the effluent discharge quality.
- Up-flow anaerobic sludge blanket (UASB): It is popular due to its low energy usage, easy maintenance and cost-effectiveness. However, when used in isolation, UASB reactors do not produce good quality effluent. It needs to be complemented with other technologies.
- Down-flow hanging sponge (DHS) reactors: These help in post-treatment of effluent generated from UASB systems. The DHS process uses polyurethane sponge as a medium to retain biomass.
- Rotating biological contactors (RBCs): These are fixed reactors, which consist of stacks of rotating disks mounted on a horizontal shaft. The disks are partially submerged in wastewater and are rotated as it flows through. They are used in conventional wastewater treatment plants as a part of secondary treatment.
Impetus for water recycling
Water recycling can be done for both domestic and industrial purposes. However, conventional treatment does not suffice domestic water quality requirements. Therefore, there is a need to develop advanced treatment methods with:
- Multiple treatment barrier approach
- Ability to remove and disinfect high degree of microbial pathogens and chemicals
- Ability to minimise the production of residual streams.
The choice of treatment depends on the desired water quality level and the availability of land. The ease of operations, capital costs, and operations and maintenance requirements also affect the choice of treatment.
Industrial or commercial water recycling has been in practice for decades. Industries use treated water for non-drinking purposes. Depending on the grade of tertiary treatment, recycled water can be used in industries for make-up in cooling towers, rinsing, heating, ventilation, and air conditioning. Industries have shifted from using drinking water to using recycled water from wastewater treatment plants. Industries such as agriculture (for irrigating plants and feeding the livestock), aluminium/steel (heat removal, and rinsing water in metal formation and finishing), chemical (heat and medium removal for chemical reactions and wash-downs) and petroleum (heat and medium removal for chemical reactions, wash-downs and oil fields) utilise treated wastewater.
There are various national-level policies advocating the need for water recycling. However, there are no standards or codes for advanced water treatment or transfer. Although the National Water Policy (2012) includes integrated water and resources management, its implementation has been limited.
For water utilities to become sustainable and successful, a strong infrastructure model is needed. The three major components of this model should be water infrastructure, governance and community involvement, and they should have the following nine attributes:
- Water resource adequacy
- Infrastructure stability
- Operational optimisation
- Capacity and leadership development
- Financial viability
- Sector resilience and adaptability
- Community sustainability
- Stakeholder engagement
- Service delivery and customer satisfaction
The way forward
Recycled wastewater needs to be looked at as a resource to meet the growing water demands. In fact, water reuse and reclamation has been practised globally and within India at different scales. It is possible to remove pollutants from wastewater using technology and make it suitable for various purposes. Thus, conventional water and wastewater systems like RBCs need to be replaced with advanced treatment systems. A new model for urban water infrastructure is required with greater focus on water reuse and recycling in the policies formulated by the government. For the successful uptake of reused wastewater, there is a need to change consumer perceptions regarding treated wastewater and its usage.
With inputs from presentations made by Uday G. Kelkar, Managing Director and CEO, NJS Engineers India Private Limited, and Anil Kumar, Associate Director, CH2M-Jacobsduring India Smart Grid Week 2018