Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - POWERSTEP (Full scale demonstration of energy positive sewage treatment plant concepts towards market penetration)

Teaser

POWERSTEP is a project that demonstrates the novel concept and design treatment schemes of energy-positive wastewater treatment plants (WWTPs), which are net energy producers. Municipal wastewater treatment in Europe requires a significant amount of energy to eliminate organic...

Summary

POWERSTEP is a project that demonstrates the novel concept and design treatment schemes of energy-positive wastewater treatment plants (WWTPs), which are net energy producers. Municipal wastewater treatment in Europe requires a significant amount of energy to eliminate organic matter and nutrients (i.e. nitrogen and phosphorus) from the sewage prior to its discharge. An average amount of electricity of32 kWh per capita per year is required to treat wastewater. Overall, the municipal wastewater sector in Europe consumes the annual power generation of two large (1,000 MW) power plants. Similarly, organic matter contained in municipal wastewater accounts for a chemical energy potential of 87,500 GWh per year, equivalent to 12 large power stations! Partners of POWERSTEP stand with the idea that a leap-frog progress in wastewater treatment processes is possible by converting sewage treatment plants into power production facilities while maintaining or improving the quality of treated wastewater.

Today, making WTTPs energy-efficient typically addresses only marginal improvements like more efficient aggregates such as aerators and pumps, or more efficient digester operations. The realisation of an energy-positive WWTP requires a combination of new concepts for wastewater treatment together with an optimised integration of existing technologies in all side aspects, including sludge treatment and biogas valorisation. POWERSTEP uses concepts and technologies that have been tested in laboratories and pilot scale plants. Their full-scale commercial references with a reliable assessment of process efficiencies under realistic conditions remain at stake. POWERSTEP aims to demonstrate their viability to ensure a successful market deployment of the new technology.

• Demonstrate the concept of energy-producing WWTPs based upon full-scale investigations of individual processes and design elements.
• Assess energy balances and operation costs and the dependence on factors such as wastewater constitution, treatment quality target, and more.
• Define potential design schemes of cost-competitive energy positive and carbon neutral WWTPs.
• Ensure confidence in the design and operation of the overall treatment schemes to enable replication of solutions and rapid deployment.
• Guarantee a significant contribution from the water sector to the green-energy sector, while securing worldwide market shares and job growth in Europe.

Work performed

In the first project period (M1-18) at the wastewater treatment plants (WWTPs) of Westewitz (Germany) and Sjölunda (Sweden) two large-scale units using the Hydrotech (Veolia Water Technologies AB, Sweden) microscreen technology were built and operated to extract carbon for further biogas production which is a key element to become an energy-positive WWTP. Additional to the carbon extraction tests 50m3 reactors were constructed at WWTP Sjölunda to demonstrate mainstream deammonification using the Moving Bed Biofilm Reactor (MBBR) technology for the first time in large-scale.
Next to the practical issues a detailed literature review was carried out within the first project period that covers state-of-the-art technologies for advanced anaerobic digestion of municipal sewage sludge. The review is based on an extensive review of literature and available data, focusing on processes which have been realized in full-scale plants and includes information on single-stage mesophilic digestion, thermophilic digestion, temperature-phased digestion, high-load digestion and other process modifications, as well as mechanical, thermal, chemical, and biological disintegration methods.
For discussion on the topic “Nitrogen management in side-stream“ different technologies were tested as well as calculations of the energy demand were carried out in the first 18 months of the POWERSTEP project. For example at WWTP Kirchbichl (Austria) nitritation was implemented as a side-stream treatment process and at WWPT Altenrhein (Switzerland) pre-test were carried out to fix finally the design to construct a full-scale technical implementation of an ammonia stripping process.
Also a general approach is worked out to screen potential schemes for WWTPs in their energy profile with the energy audit software OCEAN, focussing on reference schemes as benchmark and potential POWERSTEP schemes with innovative process modules. These promising combinations of modules will then be further assessed in detail with life-cycle based tools of LCA and LCC in their environmental and economic profile.
And last but not least to promote POWERSTEP one website was created and the second one to communicate about the POWERSTEP concept in a fun and educational way using both an animated video that can be easily used on social media and presentation shadowed with an interactive website showing how integrated WWTP can be in the design of energy supply, will get online within the next two months. The overall aim of the POWERSTEP communication purpose is to offer a multi-channel user journey that will strengthen its capacity to reach out from the general public to the expert community.

Final results

The technical objectives in POWERSTEP are very ambitious, and auditable with the SMART goals that are defined for each technology or approach investigated in POWERSTEP. Very significant progress beyond state of the art can be noted when comparing these SMART goals with today’s state of praxis:
State of the art (today)
• Energy neutrality of sewage treatment plants, max. 10% of chemical energy in wastewater recovered as electricity, periods of negative heat balances (= heat surplus wasted as off-gas heat).
• 30 to 50% carbon extraction in primary step
• Nitrogen removal via nitrification and denitrification
• 50 to 60% CH4 content in biogas
• No recovery of excess heat
• No dynamic management of power and heat demand and supply on STP
• Ammonia stripping of process water (with air, steam or vacuum process)
• Energy efficiency of single process steps

Ambition of POWERSTEP beyond state-of-the-art:
• WWTP as net producer of renewable energy (both electricity and heat), without compromising treatment performances and operation costs. Up to 20% of chemical energy in wastewater recovered as electricity, reduction of energy demand for treatment by at least 50%, at least 150%
electricity positive WWTP, no more periods of negative heat balances.
• 60 to 80% carbon extraction in advanced primary treatment, optimised carbon extraction in combination with nitrogen removal requirements via advanced control options
• Full-scale implementation of alternative nitrogen removal ( main stream deammonification, duckweeds bioreactor).
• “Power-to-gas” concept: > 90% CH4 in biogas.
• Steam rankine cycle and thermoelectric processes for heat recovery.
• “Smart grid” concept: dynamic (cost) optimisation of electricity and heat management (incl. seasonal heat storage).
• Membrane ammonia stripping: first cost estimations and pilot assessment showed economic superiority, to be confirmed in first reference.
• Integrated consideration and optimisation of treatment schemes. Proposals for existing infrastructure and “green fields”.

Website & more info

More info: http://www.powerstep.eu.