OPERATION AND MAINTENANCE OF SEWAGE TREATMENT …

1 OPERATION AND MAINTENANCE . OF SEWAGE TREATMENT . PLANTS. MAINTENANCE Scheduling MAINTENANCE of each equipment is done as the recommendations of manufacturer. A History card is maintained for each equipment so that record is maintained for equipment performance and MAINTENANCE . Good housekeeping is an important aspect of plant OPERATION . Pumping Machinery To run the machinery in a way so as to have free fall from invert of sewer. Mostly 2 or 3 pump sets are out of order. Guide Wire/ Guide Rail should be in good condition. Minimum one pump be operated during night hours so that sewers are empty in morning. Screening Chamber & Wet well Regular Cleaning Disposal of Screenings Washing of Bar Screens Washing sludge layer from walls using water jet Desilting of wet well once a year Receiving Chamber & Fine Screens Should be scoured minimum once in a week. Fine Screens should be kept clean of all obstructions. If the screen are of mat type, its OPERATION should be adjusted such that a mat is always on the screen.

2 Grit Channel (1W + 1S) grit channels for peak flow. Should be used one at a time, alternatively every day. Should be cleaned every day. Proper & efficient removal of silt in grit channel will improve the functioning of TREATMENT . Proportional Weir It is provided to maintain uniform flow on upstream and downstream of grit channel. Must be Calibrated so as to show the quantity of flow. Flow be recorded every hour. In SBR Plants the Flow recording graphs are recorded in SCADA PC. Distribution Channel Must be cleaned every day. Moving Bed Biofilm Reactor (MBBR). The STP is said to be running successfully, if:- The biofilm layer shall accumulate on the bio media. The flocs should generate in Clarifier. The smell of sludge should not be foul. When starting the plant initially, the air blowers should be operated for passing the air through diffusers and run continuously, otherwise the desired parameters will not be achieved.

3 Fill both aeration tanks to the normal operating SEWAGE depth, thus allowing the aeration equipment to operate at maximum efficiency. Moving Bed Biofilm Reactor (MBBR). Using all of the aeration tanks will provide the longest possible aeration time. The effluent end of the aeration tank should have a dissolved oxygen level of at least mg/L. DO in the aeration tank should be checked every two hours. Generally the DO is approx. above 4 in aerated SEWAGE . The COD reduction in treated SEWAGE Vs. raw SEWAGE cannot be less than BOD reduction. How to check DO in aeration Tank The presence of DO in aeration tank requires the elaborate procedure of using a meter operated electronically and keeping the probes well cleaned at all times. This is not always possible. Moreover, typical plant control requires an answer to the question of whether residual DO is present or absent in the secondary clarifier overflow. This can be easily carried out in the field as follows: 1.

4 Take a 10 ml well washed test tube. 2. Hold it gently against the weir overflow sideways. How to check DO in aeration Tank 3. Allow the SEWAGE to fill the tube and overflow for a few minutes. 4. Gently take the tube and pour out about 2 ml. 5. Add few drops of manganous sulphate solution. 6. Add a few drops of potassium iodide solution. 7. Close the top with the thumb and invert a few times. 8. Allow to stand for a few minutes. 9. If there is a yellow precipitate, DO is present. 10. If there is a white precipitate, there is no DO. With help of electronic instrument Online sensors are required to be provided Reactors /SBR. 2 in nos. (Parallel & in series). The walls, walkway and the railing to be washed daily using water jet. The problem of foam can be solved using water jet . Reactors should be desludged every day to maintain proper MLSS. Sequential Batch Reactor (SBR). The first is to make certain that all mechanical, electrical and control equipment is operating properly.

5 The purpose of Fill-React OPERATION is to add substrate (raw SEWAGE ) to the reactor. The addition of substrate or filling is controlled by a timer to a set time period. The filling OPERATION is also controlled by level transmitter to limit filling volume upto maximum level. Usually, SBR tanks are designed to take flow as it comes into STP with all variations from peak flow to minimum flow without necessiating any equalization tank. The Settling process is controlled by time and is usually fixed between 30 minutes to an hour so that the sludge blanket remains below the withdrawal mechanism during the next phase. The purpose of Decantation is to remove the clarified, treated water from the reactor. Sequential Batch Reactor (SBR). When starting the plant initially, the diffuser should be operated first and run continuously, otherwise the desired parameters will not be achieved. The precaution needed is to make sure that power supply is available continuously.

6 If power supply fails, immediately bring the genset on-line. COD to BOD ratio indicates the biodegradabitity of the SEWAGE . Normally, SEWAGE will have COD to BOD ratio between to 2. If the ratio is more than 2, entry of industrial effluents into sewer network is a possibility. The daily tests shall be COD, TSS, pH, Dissolve oxygen, Ammonia and dissolved phosphate. BOD can be a weekly test. Problem of foaming Foaming in aeration compartment in first week of start be tackled with water hose using fresh water with lawn sprinkler It will diminish when sufficient mixed liquor solids are obtained Do not waste sludge until desired level of MLSS. obtained Sludge Sump & Sludge Drying Beds Sludge from the sump be regularly pumped out. Generally the Sludge Drying Beds are empty without any sludge shows that plant is not running. Dried sludge cakes be removed regularly from Sludge Drying Beds. Compressors and VFD and DO meter (2W +1S) compressors.

7 2 compressors should continue running till desired level is achieved. Generally compressors and VFD are found out of order. Most of the times, the compressors are found not working with the excuse of power cut. At least one compressor should be in OPERATION every time in case of power cut also (with the help of D. G. set). Clarifier The treated water flow should be uniform over the entire length of the launder. It would ensure aeration also. There should be no scum over the surface. Bridge should be kept running. Sludge should be continuously removed. Launders should be kept clean. FLOW meters . Magnetic Flow meters Magnetic flow meters work on the principle of electromagnetic induction. The induced voltage generated by an electrical conductor in a magnetic field is directly proportional to the conductor's velocity. These are non-invasive and used in almost all pipelines, but initial calibration is needed. The output is the standard 4 to 20 mA signal, which is relayed to the central monitoring system.

8 Ultrasonic Flow meters When ultrasonic impulses are released onto a pipe surface carrying SEWAGE , the impulses are deflected along the flow direction based on the velocity of the flow before they impinge on the opposite sidewall of the pipe. The time taken by impulse wave is measured and is correlated to the velocity and then to the diameter of the pipeline and hence the flow rate is arrived at. Like magnetic flow meters , these are also non-invasive and used in almost all pipelines but, initial calibration will be needed. Visual Test The final effluent shall be clear and free from suspended particles. Flocs exists in the clarifier. A film exist on the MBBR Media. Sludge is produced daily. No odour or smell in the final effluent. No odour in sludge. Discrepancies observed in construction of STPs Design mix with weigh batch mixer not followed Chemical protection on the RCC not done SS pipes not checked Cement store not constructed Site office not constructed Railing not provided as per agreement Sample test register not maintained No planned execution Discrepancies observed in construction of STPs Stairs/ Steps not fitted in any of the chambers/ reactors/ sump etc.

9 V- notch weir plates not fitted around the launders. Circular peripheral wall not provided in the clarifier. Scum removal arrangement not made in the clarifier. Proportional weir has not been calibrated. Scour valves not provided in receiving chambers. Arrangement for proper disposal of screens & grits not made. Level of outlet channel is such like that water remains stagnant in the launders. VFD and DO meter have not been installed. General observations M. S. parts are not epoxy painted regularly and are rusted. Screens and grit channels are not cleaned. Both Grit channels are run simultaneously where as it should be one running & to be used alternatively every day. Pumps are not run in proportion to the discharge received. No pumps are run from 10:00 to 4:00 Sludge is not removed from reactors & clarifier. Dried sludge cakes are not removed from Sludge Drying Beds. General MAINTENANCE of the lawns etc. is very poor.

10 General observations .Contd . The sitting room & the toilet are not in good condition. set is not operated in case of power failure. O & M staff is not as per the norms qualification and experience. Industrial effluent is being received at the SEWAGE TREATMENT Plants for which no correspondence being made with Haryana State Pollution Control Board. Consent to operate has not been obtained from Haryana State Pollution Control Board. Samples are not being tested in laboratory daily. Samples are not being got tested regularly from some reputed laboratory. Quantity of BIO- MEDIA not checked with design approved by SE. Thickness and quality of SS pipes, DI pipes not checked. Originality of Electrical equipment not checked and verified. RECORD TO BE MAINTAINED BY CONTRACTOR. DURING O&M. Attendance of O&M Staff engaged by the contractor. Quantity of Raw SEWAGE / treated SEWAGE water. Quality of incoming/ treated SEWAGE water based on laboratory testing to be maintained by the contractor.