STP – Maintenance handover from Builder

“All Apartment Complexes with an STP will do well to check suitability of Treatment Technology, Adequacy of Design and good Engineering Practice in the execution of the Treatment Plant before accepting the STP from the Builder/ Developer

Is your Association in the process of taking maintenance handover from the Builder? One of the main areas to keep a tight watch on is the sewage treatment plants (STPs) and their STP maintenance. If the Builder is handing over a well-built and well-maintained STP, it can save you tremendous cost and misery in the future.

Here is an article written today by Dr. Ananth Kodavasal, Proprietor of Ecotech Engineering Company, with 25 years of experience in Building, Renovating & Auditing Waste Water Treatment Plants.

ABSOLUTE  IMPERATIVES FOR LONG TERM

SUSTAINED SATISFACTORY PERFORMANCE

OF WASTEWATER TREATMENT PLANTS

BACKGROUND

Wastewater Treatment Plants serve diverse treatment applications, ranging from the ubiquitous Domestic Sewage Treatment Plants (STP) to highly specific treatment plants, say, treating wastewater from a palm oil processing facility, pulp and paper manufacturing facility, textiles processing industry, petrochemical plant, bulk drugs manufacturing facility, all of which are commonly termed Trade Waste or Effluent Treatment Plants (ETP).

The basic requirements of any treatment facility, be it an STP or a very specific ETP, to deliver satisfactory performance over the long term, remain the same:

1. Proper Design of the Treatment Plant
2. Proper Engineering of the Treatment Plant
3. Proper Operation and STP maintenance of the Plant

All three aspects above are interdependent and can deliver performance only synergetically: in many instances, one cannot fully rectify or overcome lacunae and defects in the other two aspects of the plant.

2. DESIGN ASPECTS OF A PLANT

Various aspects to be considered in the design of a treatment plant include:

• Characteristics of the wastewater in terms of quantity and quality.
• Presence of toxicants/biological inhibitors (in case of a biological treatment plant).
• Wastewater discharge pattern (continuous/intermittent/batch dump/peaking factors/seasonal variations).
• Locational and environmental factors (altitude, temperature variations, rainfall, etc.).
• Selection of appropriate technology, treatment units, and treatment processes.

3. ENGINEERING ASPECTS OF A PLANT

Engineering aspects of a plant are related to:

• Proper and optimal layout of the plant.
• Proper and optimal hydraulic levels and level differences of various units in the plant.
• Proper selection of mechanical equipment such as capacity/rating to suit the design and engineering of the plant.
• Inter-unit piping per good engineering practice.
• Proper electrical system and cabling per good engineering practice.
• Proper placement of equipment and units for ease of maintenance.
• Proper illumination and ventilation, etc., for operator comfort, health, and hygiene, and incentive to remain at the plant for monitoring.

4. OPERATION AND MAINTENANCE ASPECTS OF A PLANT

Aspects to consider under this head include STP plant operation and maintenance, such as:

• Proper STP maintenance procedures, including regular preventive maintenance and well-documented Standard Operating Procedures (SOP), are key to ensuring longevity and efficiency of the plant.
• Developing and maintaining a Standard Operating Procedure (SOP).
• Training of operators in the SOP.
• Developing and maintaining a Preventive Maintenance Program and Checklist for mechanical equipment.
• Trained mechanics and technicians to execute the PM program.
• Developing and maintaining an operational log.
• Frequent Monitoring, Control, and Validation of the above procedures and processes by qualified and experienced Field staff from H.O of the service provider/AMC contractor.

5. TYPICAL EXAMPLES OF INTERDEPENDENCE OF UNITS IN A STP TREATMENT PLANT

Each and every single treatment unit and treatment process in the treatment plant must operate at its optimal, design efficiency for proper functioning of the sewage treatment plants. A malfunction in any one unit can have a serious and adverse impact on one or more of the other units in the treatment train. A few examples will suffice for illustration purposes, all of them ultimately resulting in poor performance of the treatment plant, directly and otherwise.

• A malfunctioning/defunct/inaccessible Bar screen (a most innocuous-looking unit) can damage the pumps in the treatment plant, leading to downtime and malfunctioning of the treatment plant (Engineering defect).
• An undersized Equalization tank will lead the operator to pump out water at higher than design rates, leading to overloading of the aeration tank and settling tank, which leads to poor performance of the plant (Design fault).
• Improper aeration/mixing in the Equalization tank will lead to solids settlement, leading to frequent choking of pumps/septic conditions in the Eq. tank, again resulting in poor treatment performance (Engineering defect).
• Selection of a submersible pump with very small internal passages for raw sewage lift duty will lead to repeated failure of pumps (Engineering defect).
• Capacity of the aeration tank is not sufficient for complete treatment of the design quantity and quality of wastewater as per good engineering and process calculations (Design defect).
• Mixing in the aeration tank is not proper due to insufficient number, size, and specification of diffusers/aerators (Design defect).
• Excessive difference in water levels of the aeration tank and settling tank leading to turbulence in the settling tank (Engineering defect), having a cascading effect:
  • Solids carryover from the settling tank.
  • Overloading and choking of the filters that follow.
  • Inability to settle and capture microbes for recycling to the aeration tank.
  • Inability to maintain the desired level of MLSS in the aeration tank.

This results in a vicious cycle starting with (i) all over again.

• Undersized Filter press for sludge dewatering will result in the inability to maintain proper MLSS levels in the aeration tank, resulting in the same cascading effects described above.

6. SUMMARY AND CONCLUSION

• In summary, proper Design, Engineering, and STP plant operation and maintenance are absolutely imperative for the successful and satisfactory performance of a treatment plant in the long run.
• Each and every unit must perform at its optimal and most efficient design level for overall satisfactory performance of the plant
• Each and every unit in a treatment plant directly or indirectly impacts performance of other units in a treatment plant
• No unit or process in a treatment plant may be considered as being of secondary importance due to synergy between units as described above.
• All Apartment Complexes with an STP will do well to check suitability of Treatment Technology, Adequacy of Design and good Engineering Practice in the execution of the Treatment Plant before accepting the STP from the Builder/ Developer.

Dr. Ananth S Kodavasal

April 13, 2011

Ecotech

Dr. Ananth/Ecotech can be reached at ecotech.bangalore@gmail.com

Note: This article was published by Dr. Ananth in the WaterBLR ADDA, a Forum for Leaders from various Associations in Bangalore, to discuss Water Management issues. If you are an Association Leader and wish to be part of the WaterBLR forum, please write to support@adda.io with subject ‘WaterBLR’.

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