Integrated anaerobic system for wastewater reclamation at ambient temperature in European climates

PROJECT DESCRIPTION

BACKGROUND

The growing problem of scarcity of water of sufficient quality affects around 70% of European citizens, especially those in southern countries where the impact of climate change is greater. In fact, some are living in extreme situations with increased frequency of flooding or drought. As the cost of energy production increases, so too does the cost of water. As a result, EU policy-makers and institutions are committed to developing new strategies that encourage efficient use of water resources. The European Innovation Partnership on Water, (EIP Water), created in 2012, has identified priority areas in order to overcome the main environmental problems related to water: scarcity, unsustainable wastewater treatment and the impact of untreated wastewater on water bodies.

OBJECTIVES

The LIFE SIAMEC project would demonstrate the anaerobic treatment of municipal and industrial wastewater at ambient temperature in European climates in order to obtain a technology that consumes less energy, produces less biomass and has a lower integrated footprint for wastewater reclamation. This technology would overcome the main drawbacks associated with anaerobic wastewater treatment at low temperature – namely, greenhouse gas emissions and nitrogen removal – since the dissolved methane present in the effluent is used as a source of carbon for denitrification in both a membrane and a non-membrane based post-treatment.

The project would demonstrate the technical feasibility of applying basic and advanced reclamation processes to the effluents of both prototypes for agricultural, industrial, environmental and urban water re-use while reducing associated costs and environmental impacts in comparison to the conventional wastewater treatment schemes currently applied.

 

RESULTS

The LIFE SIAMEC project demonstrated at prototype scale the patented SIAM technology for the integrated anaerobic treatment and reclamation of wastewater, with nitrogen and dissolved methane (CH₄) removal. This new solution utilises recovered bioenergy in a new denitrification process, with methane as an electron donor, to generate a lower amount of biosolids. The project team demonstrated the approach with municipal and dairy wastewater, allowing water reuse for agricultural, urban and industrial applications.

 

The Mediterranean urban wastewater demonstration site was at the wastewater treatment plant (WWTP) of Cabezo Beaza (Cartagena, southeast Spain) operated by Hidrogea, which has a nominal capacity of 35 000 m³/day. The project’s prototype had a capacity of over 10 m³/day in the mainstream anaerobic line, embedded in a UASB (upflow anaerobic sludge blanket) reactor. In series to the UASB, two lines were coupled as post-treatments to separate biomass and effluent by different methods (membrane and lamella settler). A tertiary treatment with a sand filter and an ultraviolet lamp followed. The main results obtained after the testing period were:

• An average value >55% of the organic carbon present in the wastewater was transformed into profitable methane-rich biogas.
• The polishing lines could deplete up to 55-60 mg TN/L and the remaining organic carbon, reaching allowed discharge limits for both (COD 125 mg/L; TN 20 mg/L).
• Nitrogen elimination values indicated the coexistence of conventional and recently discovered nitrogen removal processes.
• Effluent quality was as high that it could be, and was directly reclaimed for irrigation.

The Atlantic site industrial wastewater demonstrated site was at CAPSA Food’s factory in Outeiro de Rei-Lugo (northwest Spain), where powdered and bricked milk are manufactured. The wastewater generation averaged 1 200 m³/day. The project prototype had a capacity up to 8 m³/day in the mainstream anaerobic line, also in a UASB reactor, followed by a post-treatment with membranes. A reverse osmosis module was also installed, to obtain high quality treated water for specific reuse purposes (which also reduces demand for freshwater).

 

A life cycle assessment (and direct samplings of N₂O and CH₄) showed that direct emissions from the SIAM process were over 60% lower than for current CAS-WWTP in the Mediterranean prototype. For the Atlantic prototype, similar results were observed, with an increased level of diffuse emissions; suggesting that covering reactors or installing gas-treating filters should be considered when designing a full-scale facility. SIAM accounted OPEX-values were decreased by 20% compared to the current WWTP-CAS. Nevertheless, CAPEX was higher due to the cost of membranes; until a 6-year payback time, after which SIAM is more profitable than CAS.

 

The project team also concluded that:

• Biogas valorisation led to energy self-efficiency values larger than 50-65%, depending on performance of the anaerobic stage and organic carbon concentration of wastewater.
• Biosolids reduction larger than 40-60% were achieved with SIAM-based schemes with respect to similar CAS schemes.
• SIAM was associated with newly discovered collaborative denitrification processes, enhancing rates of nitrogen removal.
• Estimated/measured global warming potential of based-on-SIAM schemes decreased by at least 60%, with respect to equivalent CAS approaches.

Further information on the project can be found in the project's layman report and After-LIFE Communication Plan  (see "Read more" section).