ADVANCED TREATMENT
The new plant provides an additional 1.435Ml/d of biological/MBR treatment capacity
Food producer doubles its reuse capability
Water reuse is an increasingly attractive process for food manufacturers across the UK and worldwide. Geraint Catley and Steve Goodwin of Aquabio revisit an expanding site in Evesham to increase capacity
are now linked to the economics of recycling water. Charges for incoming water are rising, as are effluent disposal costs. This is in addition to limitations on borehole/surface water extraction or final discharge constraints. Recycling is therefore an increasingly attractive option and with recent developments in treatment technology, the payback on capital investment has reduced significantly, in many cases to below two years. These motivating factors are heightened by business growth and/or factory expansion and pressure from customers to reduce carbon and water footprint. Companies with existing wastewater pre- treatment infrastructure may find investment in potable recycling option more attractive. The UK Government is offering an Enhanced Capital Allowance (ECA) tax incentive scheme for water reuse investments where 100% of capital expenditure is fully allowable in the year following start-up of an ‘eligible’ efficient membrane-based plant reusing >40% of the factory wastewater.
W
Aquabio has specialised in industrial water reuse since 1998 and uses its own crossflow membrane bioreactors (MBRs) as the core process in its wastewater recycling plants. By developing three types of crossflow based MBR technology, the company can offer its clients the most cost effective alternative for their particular circumstances.
All Aquabio MBR plants have ‘true’ ultrafiltration (UF) membranes mounted outside
24 Water & Wastewater Treatment December 2010
ith the stigma of wastewater reuse in food factories much reduced, the driving issues for the sector
of the bioreactor in dry conditions which means hygienic operation, ease of maintenance and no parts immersed in the biomass. The three types of system are:
1. AMBR - which utilises high crossflow to achieve high flux rates. The bioreactor can be operated at high biomass mixed liquor suspended solids (MLSS) concentrations. The technology is aimed at lower flow and higher strength wastewaters. Plants are extremely compact, with very low membrane area and low membrane replacement costs. The membrane banks are operated automatically based on level in the bioreactor and hence are utilised, as required, to match the inlet flow. When not required, individual membrane banks are automatically shutdown, auto-
Table 1: Comparing the MBR systems MBR Type
Normal
Operating MLSS range (gTSS/l)
AMBR AMBR LE
10 to 20 (Air) 15 to 35 (Pure oxygen ‘enhanced)
10 to 20
Sustainable Normalised flux LMH
80 to 250 40 to 120
flushed to remove biomass and await re-start thus saving energy when the plant is not running at full design, or when membrane flux is higher than design. AMBR plants are modular, can be containerised and are relatively low in capital investment cost.
2. AMBR LE - which utilises intermittent backflushing for the control of membrane fouling and hence allows a reduction in crossflow velocity and a significant saving in energy. Medium to high MLSS concentrations are accommodated and AMBR LE is aimed at medium to high flow and low to high strength wastewater. With variable speed recirculation pumps the system allows for a ‘managed’ flux rate which is used to optimise energy consumption relative to the plant load. Plants
Energy use on biomass separation kWh/m3 permeate produced
1.8 to 3.5 0.25 to 1.4
Configuration/ maintenance
‘Dry’, out of tank. Low level, horizontally mounted membranes
‘Dry’, out of tank. Low level, horizontally mounted membranes
BIOVERT
Submerged HF/Flat Sheet
8 to 15 6 to 12 30 to 60 8 to 25 0.2 to 0.5 0.6 to 2
‘Dry’, out of tank. Vertically mounted membranes
Submerged in
biomass & vertically mounted with course air scouring from below
Energy management
Yes. Banks are automatically flushed & shutdown on low/no flow
Yes. Permeate flow automatically regulated & banks can still be automatically shutdown on v. low/no flow
Yes. Banks are automatically flushed & shutdown on low/no flow
No. Membranes submerged in biomass and must be regularly ‘scoured’. Energy can be >2kWh/m3 during very low/no flow.
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