PROJECT DESCRIPTION
BACKGROUND
More than 500 million people in Europe generate around 27 billion m³ of municipal wastewater each year. Municipal wastewater treatment plants (WWTPs) consume large amounts of energy. For example, WWTPs in Germany use around 4400 GWh/year, the equivalent to roughly 1% of the country’s total net electricity consumption per year.
Currently, most WWTPs use aerobic processes which consume a considerable amount of energy. Bioreactor aeration can use as much as 60% of total WWTP energy consumption.
Costs related to such wastewater treatment are expected to rise due to increasing restrictions on the discharge of treated water (EU Water Framework Directive 2000/60/EC) and sludge disposal. Such restrictions represent a significant challenge for treating wastewater. Furthermore, new regulations related to the mitigation of greenhouse gas emissions could penalise both energy consumption and sludge production.
OBJECTIVES
The LIFE MEMORY project aimed to demonstrate (at an industrial prototype scale) an anaerobic technology, using the innovative Submerged Anaerobic Membrane Bioreactor (SAnMBR) technology, as an alternative to traditional urban wastewater treatment. The SAnMBR technology combines anaerobic digestion and membrane technology, allowing for the treatment of urban wastewater at ambient temperatures. Anaerobic digestion allows the conversion of the organic matter into a biogas flow (composed mainly by CH4 and CO2) that can be used at the WWTP to generate heat energy and electric power. On the other hand membrane filtration allows the sludge retention time (SRT) to be increased by 100% without increasing the reactor volume – thus in turn permitting anaerobic processes to be used for low-loaded wastewaters. Low growth rate of anaerobic bacteria coupled to longer sludge retention time reduces sludge production, so that there is less residual waste to be disposed of and fewer emissions.
This new approach focused on a more sustainable concept, where wastewater converts into a source of energy and nutrients, and also a recyclable water resource by membrane disinfection.
The project aimed to demonstrate the economic feasibility of using SAnMBR technology for treating urban wastewater in a pilot plant consisting of an anaerobic reactor with a total volume of 7m3 connected to two membrane tanks, each one with a total volume of 1m3.
RESULTS
The LIFE MEMORY project created a full-scale pilot facility at the Alcázar de San Juan urban wastewater treatment plant to demonstrate that submerged anaerobic membrane bioreactor (SAnMBR) technology represents a viable and sustainable alternative to conventional treatment processes. This new approach, which combines anaerobic digestion and membranes, re-uses wastewater as a source of energy and nutrients, as well as water resource. The project team first performed simulations under a range of parameters (i.e. solids retention time, biogas recycling rate, flow rate and temperature) to calculate the optimum UV and UPV specfications for the flow process diagram for the SAnMBR prototype.
The prototype was then installed in June 2016, comprising a pre-treatment system with fine sieves and compaction of screenings, equalisation tank and mixers, anaerobic reactor, membrane tanks, degasification system, CIP tank and chemical dosing, biogas conditioning system, gasometer, CHP system, methane recovery system and dehumidifier. The pilot plant was operational till December 2018, testing a full range of organic loads and temperature. The results showed that the technology is optimal at temperatures higher than 20°C and for effluents with high organic load.
Specific quantifiable results of using the SAnMBR technology compared to conventional wastewater treatment include:
- 70%, reduction in energy consumption;
- 80% reduction in greenhouse gas; and
- 50% reduction in waste generation.
Improving dissolved methane recovery technologies could further reduce SAnMBR's carbon footprint and increase energy production (biogas valorisation).
Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).
