Opportunities for Energy Savingsand Generation in WWTPs

Dr Recep Kaan DERELI

15.04.2021

Wastewater Treatment

• The main objective of WW treatment is to remove pollutants inwastewater to minimize its impact on environment and human health.

• A WWTP is a combination of several unit processes (pumping, aeration,mixing, heating).

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Activated Sludge

• Activated Sludge Process is the most widely used system for biologicaltreatment of wastewater (Edward Ardern and W.T. Lockett, 1913).

• It is basically an aerobic biological process in which the organic matter inwastewater is oxidized by microbial metabolism.

• It principally requires a high amount of oxygen which is supplied byaeration equipment that consumes electricity.

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Activated Sludge - Aeration

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Aeration typically consumes about 20-60% of the whole energy in WWTPs

Energy Usage in WWTPs

• In Europe, WWTPs typically consume about 1% of the totalelectricity consumption of a city.

• Electricity consumption of all 10.200 WWTP in Germany ca.4.4 TWh/year which corresponds to0.7% of the total electricity consumption in Germany.

• Municipal wastewater treatment systems in the U.S. useapproximately 30.2 TWh per year, or about 0.8% of totalelectricity use in the U.S. 5

Energy Efficiency in WWTPs

• Wastewater treatment has been evolving from basic sanitation to a resource recovery concept.

• Today, it is even possible to operate WWTPs with energy neutrality and to recover several products (water, nutrients, biopolymers and biogas) out of sewage.

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EnergyConsumption

EnergyProduction

100%

40%

EnergySurplus

DWA-A 216E, 2015

Road to Energy Autonomy in WWTPs

Energy Efficiency Energy Recovery

• More efficient electromechanical equipment (pump, blower, centrifuge, etc.)

• More efficient aeration (e.g. membranes, vortex aerators)

• Process optimization (e.g. SRT, recycle flows, mixing)

• Process modification (e.g. AGS, PN/Anammox, low DO BNR)

• Instrumentation, automation and control (e.g. VFD, sensors, DO control)

• Carbon capture and diversion to AD

• More efficient AD of sludge (Thermal/US disintegration)

• Codigestion (Food waste, FOG)

• More efficient energy recovery units (CHP, SOFC)

• Heat pumps

• Sludge incineration

• Micro-hydro power

• Power H2 CH47

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Reducing Aeration Energy

Membrane Aeration• Bubbleless diffusion of O2

through a polymeric membrane

• Up to 95% O2 transfer efficiency

• A unique biofilm growth

• Improved nitrification

Vortex Aeration• Increased mass transfer of O2

with a cyclonic flow

• Aeration and mixing in a single system

• Potential to recover 30% of the energy used

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Re-visiting gas transfer efficiency

Co-digestion

• AD is the core process that leads to energy self-sufficiency.

• Sludge digesters in WWTPs are generally oversized and low loaded reactors.

Co-digestion

• Co-digestion can significantly boost methaneproduction.

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Grüneck WWTP, Germany (Macintosh et al. (2019), Applied Energy, vol. 242, 797-808)

Power H2 CH4

Power to Hydrogen

• 4𝐻2𝑂 + 𝑒− → 4𝐻2 + 2𝑂2

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Hydrogen to Methane

• 4𝐻2 + 𝐶𝑂2 → 𝐶𝐻4 +𝐻2𝑂

Power to Biomethane

Power H2 CH4

• Power to biomethane can kill several birds with a stone• Boost methane production

• Biogas upgrading and enrichment

• Storage of excess renewable energy

• CO2 capture

• Utilization of already existing pipelines and infrastructure

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This publication has emanated from research conducted with thefinancial support of Science Foundation Ireland under the SFI StrategicPartnership Programme Grant Number SFI/15/SPP/E3125. Theopinions, findings and conclusions or recommendations expressed inthis material are those of the author(s) and do not necessarily reflectthe views of the Science Foundation Ireland.

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