Wastewater Treatment: The Art Of Technology Selection
Be it municipal or industrial, clients are always choosy and sensitive about the type of technologies they select for wastewater processing facilities. When it comes to physical, chemical, or biological treatments, plant operators and supervisors look for the best available, most cost-effective, and most user-friendly alternative. As such, technology selection is an art of choosing, arranging, and weaving different components of the treatment plant to provide it a unique identity. It’s the basic building block that bestows a facility its heart and soul.
Technology selection, be it for new plants or upgrades to existing ones, is always a challenging task for the staff, engineers, and designers. Footprint requirements, accessibility, hydraulics, treatment efficiencies, capital costs, O&M needs, climate conditions, and many other factors come into picture during the decision-making process. Contemplating on such aspects at an early stage can greatly simplify project execution and minimize dilemmas that environmental professionals typically face for technologies selection.
The first opportunity in this direction arises during the planning process. At this juncture, water experts have the ability to review different products or processes available in the market, compare them, and identify potential alternatives that can suit the treatment facility’s needs. During such analysis, it is important that planners understand the extent to which plant modifications are required. Project-to-project, the scope may vary widely, ranging from simple fixes within existing tankages all the way to building brand new wastewater treatment plants on new sites. Depending upon the goals, specific technology selection approaches can be devised to pave the way for further implementation steps. A comprehensive thought process can lead to effective designs and minimize issues down the road.
As the project enters the design and execution phases, challenges become more clear and obvious. Upgrade projects may come across features like uninterrupted operations, construction sequences, accessibility for mobilization and demobilization, permit compliance, equipment clearances, existing site constraints, and so on. Newer constructions can add different sets of needs like land location, public resistance, site grading, topography, road accessibility, subsurface conditions, rocks removal, traffic management to the construction site, and more. A wide array of complexities including regulatory and compliance challenges may arise as the projects move ahead. Such evolving factors and background information can greatly impact the technology selection process. Apart from administrative, social, regulatory, financial, and site considerations, other parameters that influence technology are the actual design parameters — plant size, flow capacities, contaminants loadings, effluent limits, type of discharge waterbodies, and so on. Once the problems, challenges, and criteria are narrowed down, the selection of the appropriate technology to satisfy project demands gets underway.
Generally, wastewater treatment plants (WWTPs) utilize primary, secondary, and tertiary treatment steps for sewage processing. Primary treatments mainly rely on physical processes for water cleansing, and such methods have a long and rich history within the wastewater industry. Today, a wide range of headworks-related systems, packages, and stand-alone equipment are available for rags, suspended solids, and grit removal. Screening and grit-removal technologies are well-established and customers have many options to choose from; systems can be manual or fully automated with advanced controls, suited to project preferences and budgets. Selection of a specific technology may depend upon factors such as: type of influent sewage (sanitary or combined), presence of inflows and infiltration (I&I), expected solids loadings, minimum screen sizes, grit removal efficiencies, pumping needs, redundancy requirements, etc.
Secondary treatments are comparatively more complex and typically involve microorganisms to achieve solids and organics removals. Biology is sensitive to changing wastewater environment and weather conditions, so process selection becomes a critical step. Adopting a specific technology may depend upon wastewater characteristics like pH, temperature variations, organic and solids loadings, nitrogen or phosphorus concentrations, and coliform density. Additionally, parameters such as industrial flows, effluent quality requirements, chemical dosing needs, operational difficulties, automation, staff requirements, footprint, tank sizes, aeration needs, costs, and several other key aspects can affect the technology decision. In terms of established processes, oxidation ditches, aerated lagoons, membrane bioreactors, sequencing batch reactors, and similar sophisticated biological techniques have been implemented at wastewater treatment plants across the globe. Smaller townships or villages with lenient effluent limits, however, have opted for simpler and less-mechanized systems such as constructed wetlands, passive lagoons, and other comparable methods. With a lot of research and development taking place in the secondary treatment area over past several decades, manufacturers are now offering innovative solutions, high-tech systems, and superior controls.
Tertiary treatments for nutrients removal are quite often used by treatment plants with stringent effluent limits. Several biological nutrients-removal technologies have been deployed to date. Chemicals are also commonly supplemented for phosphorus removal. Tank sizes, configurations, recycling needs, automation, integrations, supporting infrastructures, and many parameters become the food-for-thought while selecting a specific technology. Tertiary filtration, polishing ponds, disinfection, and other methodologies are also implemented to ensure that final water quality meets regulatory needs and can be safely discharged to the environment. Reliance on chemical-based systems (such as chlorine or ozone) and the use of ultraviolet radiation to kill or inactivate microorganisms are some of the well-known choices that operators can come across while selecting disinfection systems.
In today’s world of competitiveness and cutting-edge technologies, an extensive variety of products are available for every kind of unit operation or unit process involved in the wastewater industry. Each system has its own pros and cons. Knowledge and information gained from manufacturers, sales representatives, and vendors via personal interactions, presentations, and conferences can sometimes be overwhelming, thus leading to dilemmas during technology selection. It’s always good to have multiple options available for a given application, however. Ultimately, an educated decision and long-term vision can ensure that facilities are provided with the best possible equipment and technologies.
Archis Ambulkar is an internationally acclaimed water expert and author of the well-received book “Guidance for Professional Development in Drinking Water and Wastewater Industry”, published by the International Water Association (U.K.). He has made vital contributions towards Oxford University’s Research Encyclopedia on the topic “Nutrient Pollution and Wastewater Treatment Systems” and Britannica Encyclopedia for its "Water Purification" and "Wastewater Treatment" sections. Mr. Ambulkar has written numerous international publications and participated with United Nations programs.