The village of Nimeta is located 15 km near the city of Baroda, India. There is a Water Treatment plant at Nimeta which treats 45 MLD water from Ajwa Sarovar.

A visit to Nimeta Water Treatment Plant was organised by the staff of Civil Engineering Department, GCET on 10th February, 2017. We reached there by 10 AM. At first, we were explained about the source of the water (i.e. Ajwa Sarovar) and then the flow diagram of the entire treatment plant was shown and explained in brief. Then treatment plant was explained by the super visor in detail.

The first unit for the treatment process was the sedimentation tank and the flocculator. There were 9 units of Sedimentation Tank and 12 units of flocculator. There were 6 pedals each 6 ft. wide and 22 ft. deep weighing 12 kg in the flocculator. Addition of Alum was only done during monsoon season otherwise the flocculator works as a sedimentation tank.

After the flocculation tank the water reaches to the rapid sand filter tank. There are 10 filter units each 25 ft. deep. The filter unit consists of a fine sand layer, coarse sand level and gravel level each layer 1 ft. deep. In every 4-5 hours, backwashing is done for 30 min. After the filtration process, Chlorination is done. Normally 2500 gm chlorine per hour in the form of liquid gas was added. But as the turbidity increases, they increase the chlorine dose. The maintenance work of this treatment plant is done yearly before monsoon and the treatment plant shuts down for 10-15 days for maintenance.

The visit of this treatment plant was very beneficial to the students as they could practically see the treatment process which helped them understand the concepts better. After the water treatment plant we headed towards the Atladara Sewage Treatment Plant.

We reached the Atladara Sewage treatment plant by 1 PM. We were then divided in 2 batches and were explained all the units. The Atladara STP treats 43 MLD Sewage and then releases the treated water in Vishwamitri River. The sewage from the main pumping station comes into the inlet chamber where the bar screen is provided at an angle of 45 degree. The screen removes all the floating matter like paper, plastic bottles, wood pieces, braches of trees etc. which are then disposed directly through a belt conveyor. Then the sewage is entered into the Grit Chamber which consists of pedals moving with low rpm (i.e. slow stirring). When the amount of grit increases, the sewage is taken to the grit classifier and it rotates such that all the grit is collected at one side. After that the velocity of sewage is increased by using parshall flume. Then the sewage enters into division box-1 where further the sewage is distributed evenly in 3 other division boxes for further treatment.

UASB (Up-flow Anaerobic Sludge Blanket) technology is used for the Secondary treatment process of sewage. Here the sewage enters from the bottom of a blanket of sludge where anaerobic degradation of sewage occurs and methane gas that is released through this process is taken to the biogas plant through a pipe and carbon dioxide is released in the atmosphere. Further the sewage is taken to the Pre- aeration tank where the sewage is mixed constantly and then is taken to the aeration tank where the activated sludge is added to the sewage along with oxygen for aerobic degradation. Pedals are provided in this unit for proper mixing of sludge with the sewage and aerated water is passed through surface aerators.

Further the sewage is taken to the secondary clarifier where slow stirring is done. The sewage enters into circular clarifier tank from the centre and then is distributed towards the circumference of the tank. Due to the slow stirring, Sludge is collected at the centre of the tank and clear treated water is then released in Vishwamitri River. The sludge from the clarifier can be again used in the aeration tank and parts of it is taken to the sludge thickener and then to the sludge drying bed where addition of chemicals is done and fertilizers are prepared.

Various tests like BOD test, COD test, DO test, MLSS, MLSV, etc. are performed before and after the treatment of sewage. The inlet COD of sewage is around 400 mg/L and after the treatment it is around 100 mg/L. Also the BOD of the outlet after treatment is less than 20 mg/L.

Department: Civil Engineering