WWTP Birsfelden

Twitter icon
Facebook icon
LinkedIn icon
Hybrid Ceramic Membrane Filtration at the WWTP Birsfelden

Location: 

Freulerstrasse 1, CH-4127 Birsfelden, Switzerland

DEMEAU Technology: 

Overview of the utility: 

Within DEMEAU, a hybrid ceramic membrane filtration (HCMF) will be operated on effluent wastewater treatment plant (WWTP) ARA Birs (Basel Landschaft, Switzerland). The hybrid system contains powdered activated carbon (PAC) adsorption and microfiltration by sub-merged ceramic membrane modules. The unit is a pilot scale installation with a capacity of around about 50 – 100 L/h and a total membrane area of around 2 m².
Relevant application areas of the HCMF
The application area of the hybrid ceramic membrane filtration at the WWTP Birsfelden is the advanced tertiary treatment of municipal waste water. Its aim is the significant reduction of number and concentrations of micropollutants in the final effluent before its final emission to the Rhine River.
Other options for the application of HCMF processing are the production of drinking water from surface or groundwater, the purification of industrial process water or WWTP effluent for reuse by removal of contaminants, and the pretreatment of surface water for groundwater replenishment.

Description of current system design and key figures: 

The system has been extended in January 2014 by a pilot-scale hybrid ceramic membrane filtration stage (Figure 2) subsequent to the secondary treatment of the WWTP.
Part of the effluent from the secondary treatment stage is mixed with powdered activated carbon (PAC) at concentrations of 2-4 g/L in an open 150 L-contact reactor. PAC adsorbs organic micropollutants and therefore is an effective way of reducing the amount of these pollutants in the plant effluent. Submerged ceramic membranes (microfiltratation with pore size: 0.2 µm, surface area: 0.8 m², supplied by ItN Nanovation AG, Germany) retain the activated carbon. The formation of an activated carbon scale on the membrane surface is reduced by the injection of compressed air below the membranes. Secondary benefit of the activated carbon treatment is an improved phosphorus removal potentially decreasing the amount of ferric chloride used for phosphorous precipitation while the membranes also retain bacteria and small solid particles like microplastics.
After a hydraulic retention time (HRT) of 2-3 h and an activated carbon retention time of 24 h, the activated carbon along with 5 % of wastewater is drained and fed into the secondary treatment step (activated sludge tank). In the activated sludge tank, further adsorption of micropollutants and phosphate onto the activated carbon takes place. During chemical phosphate removal, PAC is precipitated along with phosphate and removed with the waste sludge. Part of the membrane permeate is stored in a tank for backwashing purposes. The membrane flux is reversed to remove activated carbon particles from the membrane surface for 30 seconds after each 570 seconds of filtration.
Chemically enhanced backwash (CEB) is performed on a regular basis in order to remove organic matter deposited on the membrane surface. Once a significant increase in transmembrane pressure (TMP) is noticed, intensive chemical cleaning is carried out in order to recover the original membrane permeability. The CEB and intensive cleaning include the addition of chemicals like sodium hypochlorite (NaOCl).

New system design and removal mechanism: 

Description of current system design and key figures
The current system of the WWTP ARA Birs consists of mechanical cleaning (bar screen, sand trap, grease trap, fine screen and pumps), biological treatment (activated sludge tank and pumps) and phosphorus elimination (precipitation in the activated sludge tank by ferric chloride (FeCl3)). After thickening, sludge is used to produce biogas at the WWTP. The biogas is used on site to produce thermal (5’335 MWh per year) and electric (1’800 MWh per year) energy in a combined heat and power plant. About 6’000 tons of residual digested sludge per year are drained, dried and subsequently combusted.
Key figures (current system): Waste water capacity: 150’000 p.e.
Daily waste water treatment: 33’000 m3/day
Energy demand (electric): 10 MWh/day
Energy demand (thermal): 4 MWh/day
Energy production (electric): 5 MWh/day
Energy production (thermal): 15 MWh/day
Chemicals demand: 750 t/year
Residence time water: 1 day
Organics removal: 95 %
Ammonia nitrogen removal: 99 %
Total nitrogen removal: 80 %
Phosphorous removal: 90 %

Short form: 

WWTP Birsfelden