Removal of smell in STP- Hydrogen sulphide is smelly but removal of smell is easy
Sewage treatment plants have evolved to protect the environment from the adverse effects of indiscriminate dumping of raw sewage into land and natural water bodies.
As treatment norms for sewage and wastewater become more rigorous, technological options for their treatment have advanced considerably. With numerous options available, customers often find it challenging to determine which treatment option is best suited to their specific needs.
In our view, any sewage treatment technology should be designed in a way that achieves the required pollution control standards through the simplest means possible. Additionally, it should be flexible enough to adapt to changing conditions of flow and contaminant compositions.
Every sewage treatment technology can treat sewage to the required standards when designed properly. The current popular treatment systems on the market require air for treatment and include ASP, Extended Aeration, FBR, FBBR, MBBR, MBR, and SBR. Many proprietary treatments are available but fall within the categories above. Although there are anaerobic processes available, they are not very effective in meeting present pollution control standards.
For the sake of analysis, we would compare the most common and popular technologies in the market, MBBR, MBR, and SBR have been considered. All 3 three technologies have gone through many innovations to meet the present pollution control norms.
MBR (Membrane Biological Reactor)
The treatment process involves using an activated sludge process to reduce pollutants in sewage by providing aeration to a reactor. The reactor is then extended to provide extra volume to accommodate submerged membranes that filter the treated wastewater. While the activated sludge process is responsible for reducing the pollutants, the membranes effectively filter the treated water with very low levels of suspended solids. This water can then be further disinfected and reused. The membranes that filter the water use pumps with high vacuum to filter the water and also use aeration to remove the solids that attach to the membrane surface.
MBR process thus uses 2 times the air required and 3 times the energy needed as compared to an activated sludge process in its operation. The sewage treatment plant also requires high levels of operational and maintenance skills due to the complexity involved in membrane cleaning and backwashing. Although most plants are automated in operation, there is a constant need for an operator to analyze the membrane's health and performance.
MBBR (Moving Bed Biological reactor)
The MBBR (Moving Bed Biofilm Reactor) system utilizes carrier media to provide a large surface area for microbial growth. Aerobic microbes attach themselves to the carrier media and consume pollutants in incoming wastewater. The advantage of MBBR is that it is capable of treating wastewater in a small reactor volume and is capable of high levels of pollutant removal effectively and to an extent efficiently. The disadvantage of MBBR is that is very unstable when there are highly fluctuating flow conditions. Moreover, there are many badly designed MBBR plants in the market, and with the new pollution control norms where ammonia removal and phosphate removal are mandated, MBBRs should have additional anaerobic and anoxic treatment tanks in addition to aerated reactors. This would make the design of MBBR larger, eliminating the very advantage of low volume that is considered in their design.
The johkasou treatment method, despite its Japanese name, is no different from MBBR in terms of its underlying principles. These systems are popular in Japan and other countries where there are less stringent treatment requirements and energy efficiency is not a top priority. Given that Japan relies heavily on nuclear energy for power supply, the energy costs associated with running johkasou are not as high. However, johkasou are unsuited for energy savings when low or no inflow conditions exist. In addition, johkasou are inflexible and unable to handle shock loads effectively.
Extended aeration process
The extended aeration process is a treatment method that uses activated sludge to achieve good results. However, it is very energy-intensive and not designed to remove phosphates and nitrites without the addition of extra tanks or processes. As such, it is frequently used by professionals who prioritize treatment outcomes over energy efficiency. In Middle Eastern nations where energy costs are less of a concern, many extended aeration process treatment plants can be found.
SBR (Sequencing Batch Reactor)
SBR plants are designed to treat sewage in batches using a timed sequence of anaerobic, anoxic, and aerobic treatments in the same reactor or aeration tank. This eliminates the need for physical tank upgrades required in other technologies like MBBR (Moving Bed Biofilm Reactor) and MBR (Membrane Bio-Reactor). SBRs are flexible and automated, providing an advantage over other treatment methods. They can achieve pollution control norms at the biological stage and after simple sand filtration, followed by disinfection, the treated water can be reused and recycled. SBRs are often programmed to select different treatment processes depending on incoming flow and organic loadings.
EcoSBR is an adaptation of SBR with a highly efficient treatment process that does not use any mechanical device in treatment. Underground tanks are suitable for EcoSBR installations where all moving parts are outside the tank and there are no pumps or moving parts in the tanks. Aeration is provided only to reactors, unlike other plant designs. There are more than 1300 installations and EcoSBR plants are sold in 16 countries due to high efficiency. The operation and maintenance expenses are very low when compared to other technologies that are operator-dependent.
Some new treatment methodologies can be used to improve the efficiency and effectiveness of existing wastewater treatment processes, such as the aerobic granular sludge process and the IFAS process. These new methods can increase the treatment volume and enhance treatment values without requiring additional tank construction investment. While these treatment processes are currently popular in larger STPs, they will soon be available in smaller applications as well.
Then there are many proprietary treatment technologies promoted by companies that are either one or a combination of the above treatment methodologies.