The water resources for CHP systems work together to create a reliable and efficient energy source.

By understanding how these resources work individually and together, you can better utilise this renewable energy source for your facility. Each component of the CHP system needs to be considered when designing or upgrading your system.

Let’s take a closer look at each resource and how they interact.

How Does the Wastewater System Impact the CHP Plant and Vice Versa?

Anaerobic digestion is a waste treatment method that uses bacteria to break down organic material.

The biogas energy produced in the process can be used as a fuel to generate electricity and heat in a combined heat and power system (CHP). This thermal energy can meet digester heat loads and facility electricity, heating, or cooling.

The impact that wastewater sludge can have on biogas performance is limited, however, because most of the organics present in the system are the starting material for the digestion process (78% on average). In terms of pump-out frequency, the combination of a reduced digestate production level of 40% compared to conventional fermentation reactors and minimal impact on biogas quality from sludge should be sufficient to minimise the impact on digester pumping frequency.

On the flip side, the fuel gas production from anaerobic digestion represents a significant expense in CHP systems. Still, this cost can be minimised by optimising the digestion process through more efficient bioaugmentation and controlled sludge management techniques.

As electricity is predominantly generated at night, this energy can be used to meet digester heat loads and for facility electricity, heating, or cooling.

What Kind of Water is Used in a CHP System and What are Some of the Benefits?

Cooling water systems have become a vital component of CHP systems, with closed-loop water systems being used in 99% of installations worldwide.

Closed-loop cooling towers help improve CHP efficiency by recovering heat from the discharged water and using it to pre-heat boiler feedwater. This increases overall CHP efficiency and reduces fuel consumption.

A closed-loop cooling system can also be used to produce chilled water for air conditioning through an absorption chiller. Water may be an overlooked resource in CHP systems, but it plays a fundamental role in maintaining boiler efficiency by suppressing corrosion and scale formation.

It also ensures that boiler water is free-flowing and free of particles to improve circulation and heat transfer within the boiler. Clean water is also used to produce steam.

Without clean water, steam can become contaminated with particles that hinder heat transfer, reducing the steam system components’ efficiency, reliability, and lifespan. Water pumping is an essential part of the CHP plant, enabling the efficient operation of the various components of the system.

Water pumping for cooling and steam production requires reliable pumping systems with low energy consumption. To produce steam, the steam turbine requires water from a source other than the boiler feedwater.

This water is either provided directly from the water source and treated onsite, or it is extracted from a water source via a water booster station.

What Kind of Regulatory Requirements Must be Met When it Comes to Water Resources for CHP Systems?

The wastewater system connected to the CHP plant can be designed as a combined treatment facility that includes an onsite biological treatment process and an anaerobic digestion system.

Wastewater discharge characteristics and volume must be considered when designing an onsite biological treatment facility. Regulations governing the discharge of water and other wastes into the sewer system vary from country to country.

The CHP plant operators may require a building permit to discharge the water through the local sewer system. The discharge point for biogas plants may be subject to approval by the local sewage authority.

In the UK, the requirement to obtain a permit to discharge the biogas into the main sewer will depend on the wetness of the gas and the leakage rate associated with it. The biogas plant needs to comply with discharge regulations that govern the methane emissions of biogas plants within the area in which it discharges.

In the UK, the Environment Agency has issued public guidance for emissions of methane of 3% or less from a biogas plant into the atmosphere as odorous biogas with less than 5% methane.

What Are the Benefits of Using a CHP System with Water Resources?

Combining renewable energy with water and wastewater systems can help your facility reduce its reliance on fossil fuels and significantly save your annual energy and operating costs.

Combined heat and power systems can significantly reduce the energy needed in your facility to produce electricity or heat water. This can reduce your reliance on fossil fuels, lower carbon emissions and make your facility more sustainable.

The operation of the water systems can also be optimised, which reduces your reliance on external natural resources. In many cases, heating and cooling requirements can be eliminated.

Here is a list of benefits of using a CHP system with water resources:

  • Saving Money: Using a CHP system can help you save money by reducing your reliance on fossil fuel resources. For example, a 1C increase (1.8C in winter and 2.8C in summer) in water heating can cost between £35 and £45/MWh in the UK. Producing waste heat with CHP will lower these costs.
  • Boost Reliability: To meet their electrical needs, many sites utilise a variety of energy sources.
  • Sustainability: Locally produced and more effective than fossil fuels, combined heat and power systems can offer sustainable energy.
  • Producing Power at a Lower Cost Than Retail Electric Rates: Creating your energy allows you to do so at a much lower cost than getting it from traditional sources.
  • Replaces Cost of Thermal Needs: By supplying warmth for a location or industrial process, you can eliminate the requirement for more costly fuels like natural gas, propane, or fuel oil.
  • Renewable Fuel Source: The system generates energy from renewable resources like the sun, wind, biomass, or hydroelectricity.
  • Increases Reliability: By relying less on imported fuels prone to price swings and supply constraints, you can use a sustainable energy source.
  • Produces Useful Energy: Due to its many benefits, such as lowering greenhouse gas emissions and providing dependable on-site fuel supplies, biomass is a desirable option for businesses that use a lot of thermal energy.
  • Reduces Greenhouse Gas Emissions: Using biomass to replace fossil fuels reduces the facility’s carbon footprint and can contribute to meeting corporate sustainability goals.

How to Properly Size a CHP System With Water Resources?

CHP sizing is a complex process, and a single size is often not suitable for all situations due to differences across sites.

When designing the CHP system for a facility, there are some factors to consider. These include the capacity and output required, the steam or hot water demand, and the required heat rate or load profile.

Considering the power or energy required to run the CHP plant and the associated heat recovery equipment is important. Other factors include optimisation methods, plant size, and power unit costs.

The CHP system’s sizing will differ depending on whether the subject application is a single building or a district energy scheme. A building typically has a single profile with constant and predictable electrical loads.

For district energy schemes, the load profile varies more over time.

How Does the Cooling Process Work With the Water Resources to Keep Temperatures Regulated?

The cooling process in a CHP system can help to regulate the temperature of the water flowing through the water distribution system, providing a more efficient way of heating and cooling your facility.

The cooling system uses a closed loop chilled or cold water system on demand. The water from the cooling circuit is typically sent back into the boiler feedwater.

The cooling process is usually designed as a separate loop with pumps and pipework. Cold water can circulate back to the boiler from the cooling circuit through water heaters or heat exchangers.

The boilers’ water jackets are used to heat water to a temperature usually between 75 and 90 °C. Heat exchangers transfer heat from the waste heat from the flue gases to turn the water jacket into hot water that can then be circulated through the facility.

The cooling circuit is a closed system, meaning the cold water used can be collected and put back into the domestic water supply. An absorption chiller is sometimes used to help cool the water without using as much electricity.

Absorption chillers use thermal energy stored in water rather than electrical energy. This makes them much more energy-efficient and more sustainable than electric cooling processes.

The absorption chillers remove heat from a cooling circuit by circulating chilled water through the absorption chiller. The chilled water is circulated back into the cooling circuit and continuously repeats.

What Is the Importance of Having a Standby Generator and How Does It Interact With the Water Resources?

Combined heat and power systems can be backed up by a standby generator or a separate generator, providing the energy needed to keep the CHP system running.

During a power failure, the standby generator will kick in to supply the required power to keep the CHP system going without supplying power to the facility. This is important to know because you may only want the CHP system to provide you with the electricity you need for a time-sensitive process.

How Can You Optimise Your CHP System by Working With the Local Water Resources Authority?

Using your local water resources authority and your existing supplier (s) can help you save the most energy.

You can take advantage of incentives from your water supplier to install CHP equipment on site. You may also be able to receive reduced rates on water and wastewater tariffs.

Local water and wastewater treatment authorities should also be made aware of how CHP systems work and the benefits they can bring to a site. By working with your local water resources authority, you can ensure that your facility is more sustainable and effective.

What Challenges Do CHP Systems Face When It Comes to Incorporating Water Resources Into Their Design?

CHP systems can be used with other energy sources like solar, wind, and biomass.

CHP systems can also be designed to produce steam or hot water for heating or manufacturing processes. These different energy sources require a boiler to process them and can do so more effectively in different industries and facilities.

The challenge designers face how to correctly integrate the different energy sources into one system that can be incorporated into a facility. Integrating a CHP system into the existing on-site infrastructure can save a lot of money while also improving reliability for facilities that are already cogeneration.


The wastewater system is an essential part of the overall CHP plant.

The water resources used in a CHP system must meet specific regulatory requirements. The benefits of using a CHP system with water resources should be considered when sizing a CHP system.

The cooling process works with the water resources to regulate temperatures, and a standby generator is essential for keeping the CHP system up and running. You can optimise your CHP system by working with the local water resources authority.

However, there are some challenges that CHP systems face when it comes to incorporating water resources into their design. Contact us today if you want more information about how we can help you work with water resources to power your business.