Prefabricated Portable Sewage Treatment Package

Prefabricated Portable Sewage Treatment Package

Package plants are pre-manufactured treatment facilities used to treat wastewater in small communities or on individual properties, for example, hotels, station, hospitals, construction site, etc.

There is several treatment processes available in package form. Following system are available from FARAN Process and Energy Engineering Company:

• Extended Aeration

• Rotating Biological contactor (RBC)

• Trickling Filter & Bio tower

Extended Aeration is one modification of the suspended growth activated sludge process which provides biological treatment for the removal of biodegradable organic wastes under aerobic conditions. Air may be supplied by mechanical or diffused aeration to provide the oxygen required to sustain the aerobic biological process. Mixing must be provided by aeration or mechanical means to maintain the microbial organisms in contact with the dissolved organics. In addition, the pH must be controlled to optimize the biological process and essential nutrients must be present to facilitate biological growth and the continuation of biological degradation.

Wastewater enters the treatment system and is typical screened immediately to remove large suspended, settleable or floating solids that could interfere with or damage equipment downstream in the process. Wastewater may than pass through a grinder to reduce large particles that are not capture in the screening process. If the plant requires the flow to be regulated, the effluent will then flow into equalization basins which regulate peak wastewater flow rates. Wastewater then enters the aeration chamber, where it is mixed and oxygen is provided to the microorganisms. The mixed liquor then flows to a clarifier or settling chamber where most microorganisms settle to the bottom of the clarifier and a portion are pumped back to the incoming wastewater at the beginning of the plant. This returned material is the return activated sludge (RAS). The material that is not returned, the waste activated sludge (WAS), is removed for treatment and disposal. The clarified wastewater then flows over a weir and into a collection channel before being diverted to the disinfection system.

Extended aeration package plants consist of a steel tank that is compartmentalized into flow equalization, aeration, clarification, disinfection, and aerated sludge holding/ digestion segments. Extended aeration systems are typically manufactured to treat wastewater flow rates between 10 to 100 m3/day.

Another process for wastewater treatment is the attached growth method, which is applied in rotating biological contactor (RBC) and tricking filter (Bio tower) systems.

Must microorganisms are able to grow on the surface of a solid when organic compounds, mineral salts and oxygen are available they are anchored by means of an exopolymer based gelatinous material produced by the bacterial in side which the bacteria can, to some extent, move about. The colonization of the solid mater begins in selected areas, whence the bio film develops continuously until the entire surface of the support is covered with a mono cellular layer. From this moment on, growth is carried on by the production of new cells covering the first layer.

The oxygen and nutrients carried in the water to be treated diffuse throughout the bio film until the deepest cellular accumulations are no longer affected by the oxygen and nutrients.

After sometimes stratification occurs with an aerobic layer, where the oxygen is diffused, on top of a deeper anaerobic layer in which there is no oxygen.

The bio film process has a certain number of advantages compared to the activated sludge process:

• Less supervision

• Significant energy saving, as the air is usually supplied by natural draught through the film

• Often fairly quick recovery after a toxic shock

• Virtually silent

• Low maintenance costs and simple to operate and maintain

The operating principle of a trickling filter (bio tower) consists in allowing the water to be treated to trickle onto a mass of material with a specific surface area between 50 and 200 m^-1 and supporting a film of purifying microorganisms.

Depending on the type of the material used, there are two basic categories of tricking filter:

• Tricking filter with traditional fill, for example crushed siliceous rocks, blast furnace coke, etc.

• Trickling filter with plastic fill, often used in treatment of industrial wastewater treatment.

If the substrate fails to reach to the bio film, the microorganisms in the anaerobic layer die then undergo autolysis. In this way, their cellular contents become available to other facultative aerobic or anaerobic microorganism. When all of the substrate reserves are truly exhausted, the lyses of the   remaining cells causes the bio film to become locally detached from the surface. This surface then becomes available for a new colonization. The action of water currents on the surface of the bio film can bring about or contribute to its detachment.

FARAN Feature of Attached Growth Units, are:

•   Extremely low power demand.

•   Simple to install and commission.

•   Modular structure.

•   Odor free, clug free.

•   Fabricated in lightweight, corrosion resistant.

•   Proven practical and economic solutions for locations with resident or transient      population.

•   Quick start up and robust operation.

•   Excellent treatment efficiency.