The membrane bioreactor (MBR Membrane Bio Reactor) is a combination of a biological activated sludge process and membrane filtration.

Further advantages of this technology stem from the possibility of eliminating the unit to the sediment downstream of the organic sector.

The filtration system consists of membrane modules (eX type hollow fiber) that are immersed in the activated sludge tank. The treated water with an biological process is sucked through the membrane surface due to a pump that creates a vacuum inside the fibers.

The treated wastewater with MBR technology has levels of quality sufficient to allow re-use for irrigation or industrial purposes without further treatment (and therefore also in relation  with D.lg 152/2006).

- There are many advantages in the use of membranes and regard to the disadvantages we have solved this way:

- To decrease the incidence of 'high cost of the membranes GOST made a thorough study on the market for membranes.

- Knowledge of the biological aspects of the process, the dynamics of bacterial populations, their activity and cell viability is studied thoroughly in our laboratory.

The problem of fouling was resolved with a proper system of automation that GOST developed.

PROCESSES OF SEPARATION MEMBRANE

The entry into force of Legislative Decree 258/00 in receipt of EU directives 271/91 and 676/91 has involved the introduction of more stringent regulatory constraints with regard to nutrient removal from wastewater. In particular, the damage to the receiving water body has imposed the need for action on adaptation of existing sewage treatment plants, often characterized only by branches of biological oxidation of organic materials. However, this need for enhancement, tends to clash with the declining availability of surface for the construction of conventional activated sludge process, encouraging the growing interest in some types of treatment to shrink the volume of the process.

The MBR system is destined to become one of the most popular technologies among those used in water purification and this mainly in response to a national regulatory framework and international increasingly restrictive.

The membrane bioreactor (MBR Membrane Bio Reactor) are born by the conjunction of a biological activated sludge process with membrane filtration. Further advantages of this technology stem from the possibility of eliminating the unit to the sediment downstream of the organic sector.

To this end modules are used to filter UF and MF, usually hollow fibers immersed inside the tank activated sludge treatment plant, and such forms, which are subjected internally to a depression, permit the retention of biomass and suspended separation of a purified effluent with SS removal efficiencies of close to 100% (in particular in the case of UF membranes (with pore size of the order of 0.1 microns) is guaranteed entertainment for all types of microorganisms, including viruses) The membranes are selective barriers that allow only the passage of certain components of the mixture:

- Retentive or concentrate (rejected by the membrane)

- Permeate or diluted (through membrane)

The treated wastewater with MBR technology has levels of quality sufficient to allow re-use for irrigation or industrial purposes without further treatment (and therefore also in relation D.lg 185/2003). Unlike conventional systems, where operation and based on the ability to coalesce into flakes of mud sedimentation, MBR technology has no need to ensure sedimentation of the mud thus eliminating the settling tanks and process filtration.

Eliminating the settler (the concentration of the sludge reaches values 3 - 4 times larger compared with traditional systems) yields:

- Increasing the potential in case of adaptation of existing facilities

- Clear decrease in overall dimensions in new plant

DESCRIPTION OF TECHNOLOGY

Membrane bioreactors combine biological treatment of wastewater by a process of highly efficient solid-liquid separation such as filtration membranes. The filtration system that uses membrane modules for example type hollow fiber with a nominal pore diameter of 0.2 microns (micro-ultrafiltration) are immersed in the bath activated sludge.

The water treated by biological processes is sucked through the membrane surface due to a pump that creates a vacuum inside the hollow fiber. The same pump, at constant intervals, backwashing of the membrane by reversing the flow of permeate. To further reduce the dirt, the modules are equipped with a filtration system, air insufflation, which provides, through increased turbulence in the vicinity of the fibers, to minimize the storage of the biomass on the fibers themselves.

Biomass cannot cross membranes and therefore can be removed only for bleeding: this allows an accurate control of the age of the mud and its concentration in the tank. Furthermore it ensures a reduction of bacterial load significantly higher than the sedimentation.

The system also allows a greater degradation of refractory organic compounds. Indeed, the high molecular weight that often characterize these compounds makes them impervious to the membrane and thus significantly increasing the contact time of activated sludge in the tank, including encouragement of the development of specific microbial consortia.

CLASSIFICATION OF MEMBRANES

The membranes are classified according

- Nominal size of the pores,

- The geometric structure

- The constituent material (natural or synthetic, inorganic and composite)

The membranes can operate through the filtration process

- Adsorption

- Distribution

- Ion exchange

- Osmosis

The scope of use of membranes in the standings:

- Membranes for separation of liquid-solid type,

- Liquid-liquid

- Gas-gas

- Liquid-gas

TYPES OF MEMBRANES

Method used to classify processes based on membrane pore size characteristic of transition, assessed in statistical terms:

Microfiltration:

Removes pigments, bacteria, particelledi dimensionioni of sub-μ

D = 0.1 to 1.0 μm

Average D = 0.2 μm

Ultrafiltration

Removes bacteria, viruses, proteins, sugars

D = 0.05 μm

P. mol. Particles removed 5000 to 200,000 g / mol

Operating pressures up to 1,000 psi (10 bar)

Nanofiltration

Operate on the principle of diffusion in solution

Removes color, sugars, hardness, sulfate

Operating pressures up to 5,000 psi (50 bar)

Reverse Osmosis

Operate on the principle of diffusion in solution

Remove salts and ions with p.mol less than 200

Uses: desalination of sea water for drinking purposes, water purification for industrial

and pharmaceutical, leachate treatment

Operating pressures up to 7.000kPa (70 bar)

High pressures up to 15,000 psi (150 bar)

GEOMETRY MODULES

Module = the smallest unit containing one or more membranes and support structures, which can operate independently from the rest of the plant.

Geometrical structure is valid if it is able to minimize dirt and at the same time to increase the specific surface of the module.

Main types of modules:

- Expandable - the membrane is a continuous ribbon wrapped around a tube size, speed from 0.10 to 0.60 m / s (find drawing)

- Hollow fiber - much less than the diameter tubes (0.2 - 3 mm) require a rigid support, speed 0.5 - 5 m / s

- Module floors - membrane rests on supports spaced planes through the network space to avoid crushing the compartment of the permeate

- Tubular modules - ceramic materials, carbon or porous plastic, inner diameter of the tubes = 3 - 25 mm, speed 2 -6 m / s, line the inside of the tube

CONFIGURATION MEMBRANE

SPECIFIC SURFACE CONFIGURATION m² m³

COST ADVANTAGES DISADVANTAGES TURBULENCE CONDITIONS OF APPLICATIONS

Plane with support 400 -600 High Discrete can be cleaned ex - situ complex design

Cannot be washed against ED, UF, RO

With Expandable 800 -1,000 Netherlands Netherlands Scarce energy costs

Clean complex patterns rugged and compact

Cannot be washed against RO, UF

Tubular 20 -30 Very high Very good lend themselves easily to mechanical cleaning

Operate at high concentrations of solids high cost of installation UF, MF

Hollow fibers from 5000 to 40,000 Very low Very little can be controlled

Allow compact schemes

Resistant to high concentrations of colloidal High sensitivity to shock pressure MF, UF, RO

Flat diaphragm

The membranes are flat on two sides of a rigid support channeled said cartridge. They are made of polymer material and can operate both in the field of micro and ultrafiltration.

The cartridges are inserted into parallel forms of containment.

The modules cover the bottom, a system for injection of air through special speakers, so as to implement the so-called tangential filtration cross-flow "is needed to prevent

the deposit of mud and clogging of the filtering surfaces.

The specific scope may vary considerably, even and especially in the type of wastewater (critical flow, or the value of specific flow, below which no congestion occurs). The intake system is based on the permeate pump-priming self-regulated by an inverter / switch, typically operating in suction continues microcycles relaxation appropriately calibrated. To maintain long-term permeability, there are periodic countercurrent washing with a frequency ranging from one month to one year. With this type of membrane filtration is possible to operate even in the presence of concentrations of mud up to 25-30 gr / l

Hollow fiber membranes

The immersed hollow fiber membranes for separation at the level of ultrafiltration, and beyond that for the form, differ from those in flat panels for:

• Composition of the membranes (PE-C and / or PVDF, with non-ionic and hydrophilic properties).

• Operation told OUT-IN, or permeated with the aspiration of the interrupted for short intervals by a backwash operation.

These modules are good for the treatment of diluted wastewater (COD of 200-1000 mg / l) and concentrations of mud contained within the 10-12 kgSS / mc.

Also in this filtration system is in bypass mode, with injection of air through diffusers at the bottom of the form. The movement of individual fibers, anchored to the suction system to one or both ends, combined with the cross-flow ventilation, allows a stable glomerular filtration rate and low energy costs, significantly increased the filter surface being aired at the same d 'air blown over the membrane plane.

The cleaning cycles alternating with air are made available at high air flows (air pulsing) to ensure that solids, fibers and other particles are removed from the capillaries of the beams of the membranes.

ADVANTAGES MBR

- Faster startup (no need to wait for the growth of bacteria staple-trainers)

- There is no need for inoculation

- You can obtain high yield of abatement of the organic pollutant from the start (given the presence of SS in the sewage input)

- High quality effluent with the possibility of reusing water for:

Agricultural

Civilian use (water washing of roads)

Industrial (process water or cooling)

- Very high returns, excellent effluent quality

- Are absent from the recirculating mud

- Ability to expand sewage treatment works without requiring any new tanks

- Overcoming or minimizing the problem of filamentous bulking by

- Less sensitivity to load variations

- No need disinfecting

- High solids concentration and space artifacts

- Age of the high mud and less excess sludge production

- Plant complies with the lines of best technology applied Judah

- Is absent from the stage of secondary sedimentation, leading to savings in terms of massing and footprint

- Is it possible to achieve within the reactor biomass concentrations of the order of 15-30 gSSV / L, completely separate from the hydraulic residence times. possibility of reusing treated water

Against these advantages of the MBR, there are still several issues to be clarified, both in relation to the kinetics of biological processes that control the phenomena of membrane fouling

DISADVANTAGES MBR

- High cost of membranes (mainly inorganic), high tendency to fouling, frequent washing chemicals

- Lack of knowledge of the biological aspects of the process, the dynamics of bacterial populations, their activity and cell viability

- Problems of fouling makes it necessary to define the optimum operating conditions

to reduce operating costs, maintenance and / or replacement of modules

FACTORS INFLUENCE

1. Intrinsic resistance of the membrane

2. Transmembrane pressure

3. Hydrodynamic conditions at the interface membrane - solution

4. The permeability of the membrane can fluctuate over time given by:

5. Chemical deterioration - physical

6. Changes in characteristics of

7. Hydrodynamic conditions less efficient

8. By concentration polarization (accumulation of solute rejected at the interface with formation of the boundary layer of concentration)

9. Fouling or internal fouling (clogging of the pores) or external (occlusion of pores)

Fouling

The fouling is developed through chemical-physical phenomena and depends on the type of membrane (pore size, surface charge), the characteristics of the solute present in the (pH, fats, oils, fats) and operating conditions (T, scope and conditions of turbulence)

BIOLOGICAL MEMBRANE PROCESSES

Membrane biological reactors called MBR (Membrane Biological Reactor) were born in the 60s and consist in coupling a conventional process biomass suspended by membrane filtration.

MBR systems are classified into three main categories:

Membrane bioreactors for the separation and detention of the solids (500 cases in scale) are classified based upon their filtering unit in relation to the organic sector:

a. Drawings submerged membrane

b. Diagrams outer membranes

A and B differ in how will the operation of mechanical cleaning of the filter surface.

In both A and B is established in a system of tangential flow filtration, in which the food flows parallel to the surface of the membrane perpendicular to the direction of crossing the membrane from the filter component (Perm).

In A, the scheme is obtained through the injection of air bubbles

In B the scheme is obtained via the food with recirculating pumps

A lower power consumption (typical wastewater civil)

B typical industrial wastewater (high concentrations of pollutants and low flow)

- For the supply of oxygen without inflation of bubbles

- For the extraction of organic substances from industrial waste waters are

particularly rich in inorganic compounds such as acids, bases and salts

Our plans for water treatment systems are characterized by the turnkey.

Our experience allows us also, according to the needs of the customer to act on existing facilities with screening and functional analysis to bring them in optimum state of efficiency.