Environmental damage due to improperly treated wastewater flowing into waterbodies

By Proshakha Maitra*, Megha Gupta*, Dr Mansee Bal Bhargava** 
According to the United Nations Water and other leading organisations like World Wide Fund for Nature, almost two-thirds of the world’s population could suffer from water shortage by 2025. We know that 97.5% of total world water available is in oceans (saltwater) and only 2.5% of freshwater resources are available throughout the globe. Meaning, the water resources are definite and not expanding unlike the rising water demands. The global situation of the water crisis where water consumption is constantly increasing along with the world population, humanity has reached a critical stage that it has pushed us to look into alternative sources of water recovery. An alternative source of water is addressed by treating wastewater and reusing it. Efficient wastewater treatment methods are becoming crucial to sustainably meet the needs of both the present and the future.
Wastewater or sewage is a mix of debris, chemicals, waste materials, excreta and discharges from residences, restaurants, hospitals, industries and many more, broadly termed as domestic and industrial wastewaters that flow into the surface waterbodies or seep into the ground. The surface runoff generated after rainfall also gets added to domestic and industrial wastewaters increasing the contamination in the waterbodies and groundwater. Since, most of the wastewater contain very high concentrations of fatal and toxic substances, the chemical and biological contaminations of water have increased significantly over the last few decades and have become a major threat to public health and safety besides the health of ecosystem (Crini & Lichtfouse, 2019).
We are in the times when water is becoming an increasingly scarce resource and wastewater is considered as a secondary source of water where it can be reused in several processes and purposes after proper treatment. Wastewater treatment has become crucial in the present times as the natural purifying processes of the environment are unable to keep pace with the number of pollutants produced by the society. The environmental sustainability now largely depends on the efficient and effective wastewater treatment to protect the health of the ecosystem, aid water recycling, provide alternate source of energy, besides ensuring better human health.

A Session on Wastewater Treatment and Environmental Sustainability

The Wednesdays.for.Water session organised by WforW Foundation on, ‘Wastewater Treatment and Environmental Sustainability’, focussed on the ongoing technological and ecosystem based wastewater treatments. The session invited Dr Kirti Yankie and Andrews Jacob as speakers. Dr Suparana Katyaini moderated the session. Dr Kirti Yenkie is an assistant professor at the Henry M Rowan College of Engineering, Rowan University, New Jersey. With 10+ years of experience in the Process Systems Engineering she is leading the Sustainable Design & Systems Medicine Lab at the university. Andrews Jacob is a senior project manager at Consortium for Dewats Dissemination Society, Bangalore. With 13+ years of experience as a water and sanitation professional, his focus is on planning and implementing nature-based solutions in wastewater management, faecal sludge management, water body rejuvenation, integrated urban water management, and solid waste management. Suparana Katyaini during this session was an assistant professor at the Tata Institute of Social Science Hyderabad. The video of the session is available here.

Engineering versus Nature-Based Solutions

According to Andrews, Sewage Treatment Plants (STPs) are the most common systems which are used to treat municipal and domestic wastewater. Despite their several benefits, STPs are largely plagued due to high operational expenditures which often lead to their closure. There are several problems with the current sewage treatment systems and most of these systems are highly chemical and energy intensive. A common challenge in the functioning of the STP comes from the developmental activities which are ongoing processes as, new households and buildings gradually come up which get difficult to link them to the existing STPs through underground drainage channels for the treatment of wastewater.
This is where a decentralised systems is advocated as an intelligent approach as, the wastewater can be effectively treated at individual households or community levels. The decentralised wastewater treatment (DEWATS) systems are more appropriate solutions as they can provide comprehensive coverage of wastewater systems up to the last mile. The Consortium for DEWATSTM Dissemination Society (CDD Society) provides such decentralised systems with nature-based techniques which further minimise the cost of operation as they are not dependent on chemicals or energy.
The Nature-based Solutions (NbS) offer effective solutions through the use of naturally available materials and thus are free from the use of any form of chemicals or energy. This is beneficial in cutting down costs and thus is a highly sustainable form of operation. While the NbS require greater area than conventional methods of wastewater treatment despite that the former have several benefits over the latter approach. For example, unlike the conventional systems, the NbS does not depend on electricity for their operations, further reducing the emission of CO2 into the environment.

A typical Decentralised Wastewater Treatment (DEWATS)

The nature-based treatment of wastewater mainly comprises three distinct steps. The first treatment or the primary stage includes a sedimentation tank (a kind of septic tank) and involves separation of water and solid where the solid particles are allowed to settle as sludge at the bottom of the tank. This stage is designed to remove up to 40% of the total solid particles present in the wastewater. It usually takes place in two chambers to increase the effectiveness. The second treatment of secondary stage is mostly biological and does not include any form of chemicals. It consists of four to six chambers and wastewater is passed in a series of up-flow chambers with filter materials (gravel, slag or plastic elements). This stage is purely anaerobic in which the water is kept in a suspended way where floating microbes can eat small organic matter. This stage is designed to treat about 75-85% of the present organic matter. The third treatment or the tertiary stage involves aerobic treatment of the water in a Planted Gravel Filter. The filter consists of plants such as, Cana Indica, and Colocasia besides materials such as, graded gravels or river pebbles that are soaked up to half a meter in the water. The treatment efficiency of this stage is around 9%.

DEWATS Treatment Steps

These stages of wastewater treatment can be modified and combined, depending on the quantity of water, anticipated number of pollutants, and other factors. For example, highly polluted domestic wastewater may require six chambers of anaerobic baffled reactors and filter tanks whereas, in a moderately polluted wastewater three chambers of anaerobic filter tank may be sufficient. The nature-based decentralised treatment of wastewater usually operates effectively over long period without much power requirements, heavy maintenance, and operational costs.
The CDD Society has been successful in designing the DEWATS systems and bringing them to practice in several buildings, housing societies, townships, offices, educational institutions and rural communities. These systems have also been implemented for waterbody rejuvenation by providing a diversion channel for the sewage water and the rainwater to enter the DEWATS natural wastewater treatment system. The DEWATS have wide acceptance because of their low maintenance factor.

Nature based holistic waterbody rejuvenation, Coimbatore

India’s first Eco-restoration of 9 lakes, Coimbatore

According to Kirti, it is important to highlight the monitoring of wastewater treatment systems. from the water first collected from the communities being served and then taken to the plant for treatment to the collection pipes that often get eroded due to high pollutant concentration and sometimes even break due to the pressure of some unwanted substances in the water. If this data is collected over time and the lifetime of particular unit is determined through some matrices, then monitoring activities can be devised and sensors can be put in place to detect any damage caused. Machine learning methods alias computational techniques can be used to figure out the assessment and management by analysing the data. Thus, if the data input happens regularly, utility companies can easily monitor the need for maintenance rather than adopting a reactionary approach post-damage.
The low maintenance cost in the absence of large machines in the system that need service or repair has been the ultimate selling point of the NbS approach. There is absolutely zero maintenance required for the system daily. Based on how it is designed, the primary and secondary treatments/chambers need maintenance in few years for cleaning of the sludge accumulated at the bottom. The tertiary treatment, being based on the capacity of fibrous plants to absorb nutrients from the water, also does not require any heavy maintenance techniques. The filters require maintenance in around 4-5 years when they can be de-clogged to put back into the system after proper cleaning or removed or replaced in extreme condition.
Such decentralised systems will help the cities to reduce the pressure on the sewer lines. For example, the public toilets in the city of Trichy when designed, the underground drainage system was old and not designed to support the additional toilets. Then, the decentralised systems were put to use to help to remove the solid particles from the wastewater generated in the public toilets before discharging the water into the main sewer systems.

Synthesis of Efficient Wastewater Treatment Networks

According to Kirti, efficient wastewater treatment can be well understood and applied through Process Systems Engineering (PSE). The PSE provides meaningful insights into environment and sustainability. PSE also helps in analysing the cost-effectiveness of the infrastructure and the services. PSE is an interdisciplinary field of engineering management that focuses on design, integration, and management of complex systems over their life cycles. It encompasses multiple directions including data analysis, mathematical modelling, process design and operation, process control, optimization and risk analysis with quantification methods.
The treatment of wastewater varies considerably depending on its quantity, source as well as the concentration of contaminants. Since, wastewater is generated from multiple sources and varies greatly in the constituent contaminants. For example, the effluent produced by a food processing industry might contain large volumes of starch or food colouring substances while a pharmaceutical industry will have wastewater filled with pharmaceutical ingredients or hazardous solvents.
There are multiple options available for the treatment of wastewater, however matching the wastewater with the correct and most appropriate solution techniques remains a challenge. This is where appropriate solution requires PSE to design the best possible treatment process. The PSE design is a complex method as the number of possibilities increase with the number of contaminants present in the water and the number of technologies available for each task. For example, even when there are only 5 contaminants with 10 technologies for each task, there will be too many possible networks as shown in the figure below.

Not every network will be feasible as it will not help to reach the desired purity level or meet the required guidelines. Among the feasible networks too, some will be more cost-effective than others.
Thus, it is observed that wastewater treatment is most effective by using a stage-wise approach. Using this idea, the approach of a graph can be applied to the treatment. The P-graph (process graph) approach is based on simple graph theory which includes a set of nodes and vertices and based on certain axioms that the P-graph follows. It is a unique bipartite graph representing the structure of a process system with the operating units are denoted by horizontal bars, and their input and output materials by solid circles. It is a directed graph; the direction of the arcs is the direction of the material flows in the network; it is directed to an operating unit from its input materials and from an operating unit to its output materials.
It is a framework that uses vertices and nodes to represent materials and operating units connected by arcs. There are mainly two types of nodes - M Type which includes the materials such as raw materials, products and intermediaries; and O Type which includes operating units. Each of these nodes comprises some unique properties, for example, raw materials will not have any input going into it but will have the output arc leaving it. Similarly, the product will only have an output arc and it will be a terminal node. The operating units which are represented by horizontal bars are the technologies and, in these technologies, it also provides detailed insights on costs as well as some non-intuitive solutions can be obtained for sustainability.
Among the available networks to determine the structural feasibility, certain properties help to find which networks are more feasible as compared to the others. This is done based on certain algorithms. The various available algorithms for this purpose include Maximal Structure Generator (MSG), Solution Structure Generator (SSG) and Accelerated Branch and Bound (ABB).
Based on the contaminants of the sewage water, their inlet amount, and their required concentration in the pure stream, the maximal structure generator captures the maximum possibilities of technologies and processes to be used in the treatment of process. For example, in Figure below, the first stage of treatment involves 7 potential nodes with 8 operations and the next stage of treatment includes 18 such operations.

Constructing a Maximal Structure

Thus, the overall methodology of the P-Graph approach first involves the identification of the contaminants to model the wastewater treatment problem such as, solid, water, chemicals, metal, etc. It then formulates the input stream composition and the targets of the final product (output stream). Based on the above, the plausible technologies for withdrawing the pollutant materials are listed for each stage of separation. This structure is constructed in a stage-wise manner, starting with primary treatment operations and replicating the subsequent stages for each specific path. Finally, the ABB algorithm helps to determine the optimal and near-optimal structures by considering factors such as, cost, sustainability, and more.

P-graph Formulation

The ability of computational methods and P-graph axioms helps to solve the problem of electing the best possible wastewater treatment method within minutes. Parametric studies also help to determine the sensitivity of the given optimal method. So, if there is variation in the composition of the wastewater or the output chemical limits change then the graph can be modified accordingly. Similarly, the cost index can be replaced by a Sustainability Process Index (SPI). The SPI is the ecological footprint of a product or service unit divided by the statistical area per person. It indicates how much of the natural income a person is entitled to and how much is consumed to provide this product or service via the technical process undergoing assessment. In nutshell, the P-graph approach is an integrated approach involving design and optimization for the generation of cost-effective wastewater treatment networks and is one of the best available methods to determine complex decisions on sustainability concerns.

Discussion

Working with nature-based techniques in times when a lot of scientific methods are available to people is crucial of decentralised systems. Despite several scientific technologies available to people, nature-based systems have gained good attention since the beginning of the century when few NbS practitioners, like Andrews, were proactively involved in orientation programs on decentralised systems to make them popular. Still, it is required to conduct training workshops to bring more engineers into the practice and encourage them to work towards its implementation. Since, now such decentralised solutions are applied at a city-wide level where households, resorts and educational buildings are preferring to go for such simple systems for their easy operations and lower costs.
To focus on our core businesses, we often neglect the environmental damage being caused. Improper treatment of wastewater is one such issue where the polluted water is allowed to flow into the waterbodies without enough treatment. The session highlighted that a sophisticated monitoring system with simple basic ecosystem approach can save time, cost and energy and also provide an alternative way of treating sewage through minimal operational costs. Thus, keeping up the aim of enhancing water conversations, the session brought out the current problems plaguing the wastewater treatment systems presenting an alternate path towards a sustainable future.
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*Independent scholars and Fellow at ED(R)C Ahmedabad and WforW Foundation. **Entrepreneur, researcher, educator, speaker, mentor. Environmental Design Consultants, Ahmedabad and WforW Foundation (www.mansee.in and www.wforw.in)

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Wednesdays.for.Water is an initiative of the WforW Foundation, a think tank, built as a Citizens Collective. The idea of Wednesdays.for.Water is to connect the water worries and wisdom with the water warriors through dialogues/discussions/debates. The objective is to get in conversations with policy makers, practitioners, researchers, academicians besides the youth towards water conservation and management. The other team members of WforW are, Dr. Fawzia Tarannum (Climate Reality India), Prof. Bibhu P Nayak (TISS-Hyd), Ganesh Shankar and Vasantha Subbiah (FluxGen-Blr), Garbhit Naik, Monica Tewari, Harshita Sehgal, Monami Bhattacharya, Anubhuti Shekhar (ED(R)C-Ahmd), Vandana Tiwari, and counting. The Wednesdays.for.Water is reachable at wednesdays.for.water@gmail.com and WforW Foundation is reachable at hellowforw@gmail.com and hello@wforw.in. The WforW Foundation social media are reachable at Instagram, Facebook, Twitter, LinkedIn