Psyttalia - SCENA THP

Psyttalia - SCENA THP

 

 

SMARTech n.

Integrated municipal WWTP

Key enabling process(es)

SMART-product(s)

SMARTech4b

Psyttalia (Greece)

Sidestream SCENA+enhanced AD

P-rich sludge

Psyttalia Wastewater Treatment Plant (WWTP) is the largest wastewater treatment plant in Greece that serves the Greater Athens Area with a population of approximately 3.5 million people. Operation of Psyttalia WWTP commissioned in 1994 providing preliminary and primary treatment. In August 2004 with the completion of Phase B, Psyttalia WWTP was upgraded to provide full biological treatment to approximately 1,000,000 m3/d average dry weather flow. At Psyttalia WWTP, sludge treatment includes thickening by gravity thickeners for primary sludge and by belt thickeners for waste activated sludge, followed by anaerobic digestion (anaerobic, mesophilic, high-rate) for the thickened sludge mixture, digested sludge dewatering in centrifugal decanters and eventually dewatered sludge thermal drying in rotating drums. During 2016, a thermal hydrolysis process was installed to thermally hydrolize 50% of the total waste activated sludge produced daily. Following construction of the thermal hydrolysis process half of the total sludge produced is anaerobically digested and dewatered independently of the other half which follows conventional digestion and dewatering.

The separate treatment of sludge reject water relieves the wastewater line from nutrient loads and can result in attaining more stringent effluent standards with respect to nutrients. In the framework of the H2020 SMART-PLANT project, a novel process is applied at pilot scale for the separate treatment of sludge reject water of Psyttalia plant. The biological oxidation of nitrite into nitrate is by-passed by direct denitritation of nitrite. The process achieves high nutrient removal efficiency at a much lower energy and carbon footprint compared to conventional biological nutrient removal processes.

SMARTech4b is the key to enable the integration of the enhanced biogas recovery (by thermal hydrolysis) of sewage sludge with sidestream energy-efficient and compact nitrogen removal and phosphorus recovery. It modifies the original SCENA concept to treat the sludge reject water. The thermal hydrolysis process has been installed to treat 50% of the produced sludge, before this is sent for anaerobic digestion (AD). The integration of CAMBI with anaerobic digestion produces, after dewatering, a reject water stream that has a very high ammonium nitrogen concentration (>1.2 gN/L). The SMARTech4b was a pilot scale system that was treating the reject water produced following dewatering of anaerobically digested sludge that consists of a mixture of thermal hydrolyzed WAS and gravity thickened primary sludge.

The SMARTech4b pilot scale system was tested and validated at WWTP Psyttalia and consisted of a Sequencing Batch Reactor (SBR) that was treating the reject water from the dewatering facilities to biologically remove N and P. In order to increase the biodegradable COD/N and COD/P ratios reject water from primary sludge gravity thickeners was used. Alternatively, sodium acetate was also employed to increase the readily biodegradable COD in the reject water in order to efficiently remove nitrogen through short-cut nitrification/denitrification and to accumulate phosphorus in sludge through enhanced biological P removal via denitritation or aerobically.

Highlights and main results

  • The maximum NLR implemented during a steady-state period of operation was 0.50 kg N m-3 d-1
  • High performance for ammonia and TN removal was achieved (>90% and >75% removals respectively)
  • The pilot-scale unit operated even under not favorable conditions (under low temperatures of the mixed liquor ≺15oC, periods of limited sodium acetate availability, etc.) by decreasing the NLR to 0.25kg N m-3 d-1

Impact

  • Significant technical advancement through the 2.5-year operation of SMARTech 4b
  • Evaluation of an energy efficient treatment unit capable to treat thermally pre-treated sludge reject water under stable conditions
  • SMARTech 4b continuously operated properly within the typical variability of the reject water in terms of NH4N and P from the THP-AD process
  • A technical envelope with the best operation strategies under different conditions has been defined and evaluated
  • An algorithm for the SBR operation, was developed and adjusted during the pilot’s operation to optimize its performance

smartech4b
smartech 4b 2

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SMART-Plant scales-up in real environment eco-innovative and energy-efficient solutions to renovate existing wastewater treatment plants and close the circular value chain by applying low-carbon techniques to recover materials that are otherwise lost.

Seven plus two (7+2) pilot systems were optimized for more than two years in real environment in five municipal water treatment plants, including also two post-processing facilities. The systems were automatized with the aim of optimizing wastewater treatment, resource recovery, energy-efficiency and reduction of greenhouse emissions. A comprehensive SMART portfolio comprising biopolymers, cellulose, fertilizers and intermediates were recovered and processed up to the final commercializable end-products.

Dynamic modeling and superstructure framework for decision support was developed and validated to identify the optimum SMART-Plant system integration options for recovered resources and technologies.

The integration of resource recovery assets to system wide asset management programs were evaluated in each site following the resource recovery paradigm for the wastewater treatment plant of the future, enabled through SMART-Plant solutions. The project proved the feasibility of circular management of urban wastewater and environmental sustainability of the systems, through Life Cycle Assessment and Life Cycle Costing approaches as well as the global benefit of the scaled-up water solutions.

Global market deployment was achieved as right fit solution for water utilities and relevant industrial stakeholders, considering the strategic implications of the resource recovery paradigm in case of both public and private water management. New public-private partnership models were also explored connecting the water sector to the chemical industry and its downstream segments such as the construction and agricultural sector, thus generating new opportunities for funding and potential public-private competition.