Lower energy cost for wastewater treatment plants
Using an advanced process and energy simulator, Delprosa demonstrates how to cut electricity costs on your WWTP while maintaining effluent quality.
Maximising the benefit from the tariff
How much a tariff costs per annum is a complex question that depends on the plant configuration and how it is operated. Historical data doesn’t tell you what can be achieved using advanced price responsive control. Done well, the same treatment costs less.
The simulation model reveals what can be achieved. Processes that can wait are moved to times when energy is cheaper without losing the savings to higher peak demand. Constraints such as effluent quality or equipment limits are never compromised.
The simulation
This worked example shows the simulated result of a 55 ML/day plant with full biological treatment up to 3xADWF. The liquids stream comprises primary settling, 30 ML bioreactor with anaerobic and pre and post anoxic zones, secondary clarifiers, and disinfection before pump out from an 8ML reservoir via 500 L/s effluent pumps. RAS and dewatering return streams are included as well as internal nitrates recycle in the bioreactor. Sludge goes to an anaerobic digester with a 750 Nm3 gas holder with biogas being used through 300 kW cogen engine and boiler for maintaining digester temperature. A 200 kWp solar PV system and 2MWh BESS is included in the analysis and control scheme.
The type of problems we can solve
Will a different tariff cost less?
The plant is run under the current contract and under the alternate offer over the same time period. Energy, demand and fixed charges are reported separately, to evaluate whether there is a cost saving or not.
Does solar or a battery pay for itself?
Solar, a battery or cogeneration is added to the plant and dispatched against its own load and the tariff’s demand windows. The result is a capital cost, an annual saving and a payback.
Can load be moved without breaching effluent limits?
Aeration, pumping and sludge handling are shifted in time, and the effect is reported on the energy bill and on effluent quality against your limits in every case.
What is the best way to debottleneck the plant?
Tanks, pumps, blowers and sludge operations are checked against the loads they actually receive. Where something is undersized the run says so. The in-built sizing guide is a fast way to pinpoint issues quickly.
How the system is used to find the savings
Configure the simulator
The plant is built from your own data: inflow and load profiles, reactor zones and volumes, pump characterisation, blower and aeration limits, sludge handling and the equipment actually installed.
Load the electricity tariff
Current and alternate electricity tariff contracts are loaded, with provision for the complexities of modern commercial contract structures including volume use, network usage and maximum demand, time of use, and fixed charges.
Run the simulator
The plant runs over a specified simulated time period with five-minute resolution, and includes actual and forecast weather conditions for the site location that impact flows and temperatures.
Compare standard and price-responsive control
Every option runs both ways, so the value of operating differently is separated from the value of the tariff itself. The difference is reported case by case.
Review the results
Cost is reported line by line, with energy by process area and effluent quality against your limits in every case. A saving that breaches a limit is not a saving.
Compare cases on net present value
Cost of capital works are included in the model and cases are compared incrementally: extra capital against the change in annual cost, giving payback, net present value at your required return.