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MENA Water packaged plants are designed to treat sewage from sites as small as resorts and mine sites to larger development sites, towns, villages and even small cities. As a pre-fabricated, fully integrated system, that is simply bolted to a concrete slab the costs associated with civil construction and site installation is greatly reduced.
The following chart provides a simplified overview for the main MENA-Water MBR treatment process:
Settlement Tank with Pre-Treatment
The raw sewage is first fed to a automatic fine screen to remove screenings and fibrous materials. The screen is sized to the peak flow and is fitted with a 3mm perforated plate screen.
Then screened wastewater flows in the primary settling chamber which is sized on a retention time to settle all grit and heavy sludge (> 1 h).
Grease and fats are retained in the settling chamber by a baffle wall and are removed manually by a hand rake weekly. This process can be automated if preferred.
Fixed Bed Reactor
Pre-treated wastewater flows to a tank equipped with an aerated fixed bed. In this treatment step the key processes for COD removal and nitrification commences. The plant is also capable of intermittent denitrification controlled by the PLC to achieve nitrogen reduction.
The wastewater transfers by gravity via an submerged overflow to the anoxic tank
If nitrogen removal is required, this tank serves as anoxic zone for the denitrification process. The sewage then overflows by gravity to the aeration tank.
In the aeration tank fine bubble diffusors and mixers are installed to supply oxygen for the activated sludge process (pressurized air is fed by the blowers installed inside the container). In the aeration tank sludge concentration is maintained to be in the range of 10 g/l. Biological removal of nitrogen and phosphorous can be achieved by optimized process control of the aeration pattern (controlled cycles of anaerobic / anoxic / aerobic phases). Recirculation is achieved to the aeration tank via pumps feeding to MBR filtration chamber.
The water – activated sludge – mixture is pumped to the membrane chamber by recirculation pumps via an additional top strainer. The pumps supply approx. 3 times the filtrate quantity to the membrane chamber; excess fluid flows back into the aeration chamber. In this way, the sludge concentration and level in the membrane chamber is always kept at constant level, i.e. membrane performance is enhanced while activated sludge is maintained in continuous recycling process.
The membrane modules are a physical ultrafiltration system allowing only high quality water to pass through, from the outside to the inside. Scouring aeration is provided to keep the membrane surface always clean. Clear water (permeate) is sucked via permeate pump with a negative pressure ranging from 30 mbar to 300 mbar. Average flux rate through the membrane is designed to be 24 l/(m²h) for most typical sewage applications. Normal automatic operation sequences consist of filtration – relaxation – cycles in an approx. interval of 10 min – 2 min, i.e. permeate pump runs for 10 min. and then stops for 2 min. to allow for membrane relaxation.
Suction pressure is continuously monitored via transmitter/manometer. Increase of negative pressure indicates clogging of the membranes and implies requirement for cleaning. Key parameters are continuously measured and linked to the plant control system so the respective measures / warnings are released automatically if necessary.
The permeate pump delivers the filtered water into the permeate tank located on top of the MBR container. From there the treated water overflows via gravity to the treated water tank.
Automatic Backwash and Chemical Cleaning
Approximately every six hours clean water from the permeate tank is used for backwash operation. This means permeate pump stops and permeate flows from permeate tank back to the membrane modules. This regular process is activated automatically and enhances the overall performance of the filtration process.
Furthermore, to prevent fouling phenomenon on the membranes, approx. once per week an extended chemical backwash step (“CIP”) is foreseen. During
CIP phase, the backwash operation is performed for approx. 30 min. with chlorine solution.
A dosing system provides a chlorine solution to the permeate tank. To keep the system disinfected and to prevent re-contamination, chlorine dosing is automatically applied approx. once every two hours for a few minutes, in addition to the dosage during CIP backwash as mentioned above.
To view Technical Information on MENA Water’s Package Sewage Treatment Plant’s please select from the links below:
MENA Water is exclusively represented in New Zealand, Australia, PNG, Fiji and throughout the Polynesian, Micronesian and Melanesian Islands by the Hydroflux Group. Hydroflux’s commitment to our clients does not end with the delivery of the project and the Hydroflux Group local support teams guarantee our clients plants continue to operate at their full design capacity well into the future.