ch2mbr

Advantages/Disadvantages over Other Biological Processes

1. Advantages

·  The effluent is of very high quality, very low in BOD (less than 5 mg/l),
    very low in turbidity and suspended solids. The technology produces some of the most predictable water quality known.
    It is fairly easy to operate as long as the operation has been properly trained,
    pays strict attention to the proper operation, corrective maintenance, and preventative maintenance tasks.

·  The “simple filtering action” of the membranes creates a physical
    disinfection barrier, which significantly reduces the disinfection requirements.

·  The capitol cost is usually less than for comparable treatment trains.

·  The treatment process also allows for a smaller “footprint” as there
    are no secondary clarifiers nor tertiary filters which would be required to achieve similar
    water quality results. It also eliminates the need for a tertiary backwash surge tank,
     a backwash water storage tank, and for the treatment of the backwash water.

·  Generally speaking it produces less waste activated sludge than a simple conventional system.

·  If re-use is a major water quality goal, the MBR process will be a major consideration.
    This process produces a consistent, high water quality discharge. When followed by a disinfection process,
    it allows for a wide range of water re-use applications including landscape irrigation, non-root edible crops,
    highway median strip and golf course irrigation, and cooling water re-charge. When Reverse Osmosis (RO)
    water quality is required, the MBR process is an excellent candidate for preparing the water for RO treatment.

·  In certain instances, footprint can be further reduced because other process units such as digesters
     or UV disinfection can also be eliminated/minimized (dependent upon governing regulations).

·  Unlike secondary clarifiers, the quality of solids separation is not dependent on the mixed
    liquor suspended solids concentration or characteristics. Since elevated mixed liquor concentrations are possible,
    the aeration basin volume can be reduced, further reducing the plant footprint.

·  No reliance upon achieving good sludge settleability, hence quite amenable to remote operation.

·  Can be designed with long sludge age, hence low sludge production.

·  Produces a MF/UF quality effluent suitable for reuse applications or as a high quality feed water
    source for Reverse Osmosis treatment. Indicative output quality of MF/UF systems include
    SS < 1mg/L, turbidity <0.2 NTU and up to 4 log removal of virus (depending on the membrane nominal pore size).
     In addition, MF/UF provides a barrier to certain chlorine resistant pathogens such as Cryptosporidium and Giardia.

·  The resultant small footprint can be a feature used to address issues of visual amenity,
    noise and odour. Example MBR plants exist where the entire process is housed in a building designed to blend
    in with its surrounding landuse. This can reduce the buffer distance required
    between the plant and the nearest neighbour and can increase the surrounding land values.

2. Disadvantages

·  The membrane modules will need to be replaced somewhere
    between five (5) and ten (10) years with the current technology. While the costs have decreased over the past several years,
    these modules can still be classified as expensive. (The membranes “dry out” due to the flexible polymers leaching out,
    the closing/plugging of the pores, and the membranes becoming somewhat hard or brittle.)
    These costs are often offset somewhat when life-cycle costs for comparable technologies are examined.
    If the costs for the membrane replacement task continue to decrease then over time,
    then this process is even more financially viable.

·  In most sales pitches the MBR technology is stated as an option of replacing
    the secondary clarifier. Usually these clarifiers are operated with a single, very low horsepower motor,
    usually less than 2 HP. The electrical cost for this simple motor is significantly less than the filtrate pumps,
    chemical feed pumps, compressors, etc., of the MBR system. While this energy cost is significantly higher,
    the MBR system produces a significantly higher quality effluent that most clarifiers could never achieve.

·  Fouling is troublesome, and its prevention is costly.
    Several papers and research endeavors have concluded that up to two-thirds of the chemical and energy costs in an MBR
    facility are directly attributable to reducing membrane fouling. While this is costly to be sure,
    future advances into this area will continue to reduce these costs.

·  There may be cleaning solutions that require special handling, treatment, and disposal activities
    depending on the manufacturer. These cleaning solutions may be classified as hazardous waste depending on local and state regulations.