How can Effluent Treatment Plants Recover and Reuse Waste Heat?
Effluent treatment plants play an important role in minimising the environmental impact of industrial and municipal wastewater streams by treating the effluent before discharge. However, these plants are also major consumers of energy for processes like aeration, sludge digestion, dewatering, and pumping. In fact, energy can account for as much as 30% of the total operating costs for a treatment facility. At the same time, effluent treatment generates considerable amounts of waste heat that is typically vented or dissipated without being utilised. From the biological heat released during aerobic wastewater treatment to the thermal energy in digester gases, effluents, and residual sludges - this waste heat represents an overlooked opportunity for treatment plants to reduce energy expenditures and their overall environmental footprint.
We'll explore strategies treatment plants can implement to recover and beneficially reuse waste heat streams effectively.
Recovering Heat from Treated Effluent Streams
One of the most abundant sources of waste heat at effluent treatment plants is the treated effluent discharge itself. Secondary and tertiary treatment processes raise the temperature of wastewater substantially - often to 25-30°C or higher depending on the plant's treatment train and influent sources. By installing an effluent heat recovery system, that thermal energy can be captured and redirected before the treated discharge reaches the outfall. Common effluent heat recovery technologies include:
Heat Pumps: Using vapour compression or absorption chillers, heat pumps can extract heat from the effluent and transfer it to heat water or another process stream.
Heat Exchangers: Directly transfer heat from the effluent stream to heat water or another process fluid via a heat exchanger.
Energy Piles/Geothermal: Circulating the effluent through geothermal well bores, piping, or energy piles buried underground to store and extract the thermal energy seasonally.
The recovered low-grade waste heat can then be used to heat buildings, digesters, and dewatering processes and potentially even drive evaporative systems or power generation on-site. Heat recovery from treated effluent reduces the need for fossil fuels or purchased heat.
Recovering Heat From Sludge Treatment Processes
In effluent treatment plants with anaerobic sludge digesters, there are significant waste heat sources that can be tapped for recovery and reuse, including:
Digester Tank Heat: The biological exothermic reaction in digesters produces a constant stream of low-grade heat. Recovering digester tank heat using heat exchangers or loops can provide warmth for heating facilities.
Digester Gas Energy: Biogas produced in anaerobic sludge digesters, comprised of methane and carbon dioxide, contain thermal energy that can be recovered. Gas-to-water heat exchangers capture heat before biogas combustion.
Sludge Residuals: Dewatered sludge typically exits digesters/centrifuges at 30°C or higher temperatures. Installing sludge heat exchangers extracts thermal value before residual handling and disposal.
The recovered heat can be used directly for heating digesters, building spaces, dewatering processes and more. It can also drive absorption chillers for cooling or even small-scale power generation.
Other recoverable heat sources at effluent treatment plants include:
• Engine Heat from pumps, blowers, compressors and other equipment
• Exhaust gases from boilers, incinerators, or CHP units
• Hot drain streams and process heat rejected from treatment equipment
Optimising Waste Heat Recovery Benefits
To maximise the energy-saving potential of waste heat recovery systems, effluent treatment plants need to comprehensively identify, analyze and optimally configure recovery systems for their facility's waste heat streams. This often involves conducting an energy audit, measuring temperatures of effluents and other streams, assessing heating/cooling loads and mapping out an optimized heat recovery network to effectively collect, transfer and utilise the various waste heat streams. Properly designed systems with adequate storage and interchange between hot/cold streams can reduce a plant's energy consumption for heating and cooling by 10% or more in many cases - substantially cutting energy costs. Moreover, recovering waste heat reduces the overall carbon footprint and environmental impact of effluent treatment. Less fossil fuel combustion for heating means lower greenhouse gas emissions and other air pollution. It supports energy and sustainability goals.
Conclusion:
For effluent treatment plants looking to enhance operational efficiency and sustainability, implementing a strategic waste heat recovery system offers a valuable opportunity to take advantage of an abundant on-site resource - waste heat. With rising energy costs and pressures to minimise environmental impact, now is the ideal time to explore capturing this overlooked thermal resource.
To explore Customised commercial RO plants, Industrial RO plants, ETP or STP solutions for your needs in your areas and nearby regions, contact Netsol Water at:
Phone: +91-965-060-8473, Email: enquiry@netsolwater.com
