Wastewater is “used” water that is deposited into drains by residents and businesses. Flushing the toilet, taking a shower, and running the washing machine are all examples of everyday activities that produce wastewater. This wastewater drains down the sink or toilet or travels through a network of underground pipes known as the wastewater treatment system. It is 99 percent water, with only 1 percent of the wastewater being dissolved and suspended solid material.
The cloudiness of the wastewater is caused by suspended particles which, in untreated wastewater, range from 100 to 350 mg/L. a measure of strength of the wastewater is biochemical oxygen demand, or BOD5. The BOD5 measures the amount of oxygen microorganisms require for five days to break down sewage.
treatment is a multi-stage process to renovate wastewater before it re-enters a body of water, is applied to land, or is reused. he goal is to reduce or remove organic matter, solids, nutrients, disease-causing organisms, and other pollutants from wastewater.
Screened Wastewater from Palao Market
- Primary Treatment
Primary treatment of the wastewater is basically the 2nd step in the process. But then it is already assumed that the screening is already done before entering the primary treatment, this stage is considered to be the first step in the treatment. It allows for the physical separation of solids and greases from the wastewater. The screened wastewater flows into a settling/sedimentation tank where it is held for several hours. Beside this process, flocculants, FeCl2 and Lime, are added to attract or trap the particulates and settle down together. The process of sedimentation let the water sit around to let the flocculated or coagulated particles to settle out. The settled particles, sludge, must occasionally be removed from the tank.
- Secondary Treatment
Secondary treatment is a biological treatment process that removes dissolved prganic material from wastewater. The partially treated wastewater from the sedimentation tank flows by gravity into a rotating biological contactor. Here it is mixed with solids with microorganisms that consume the remaining organic matter in the wastewater as their food supply. The RBC process involves allowing the wastewater to come in contact with a biological medium in order to remove pollutants in the wastewater before discharge of the treated wastewater to the environment. A rotating biological contactor is a type of secondary treatment process. It consists of a series of closely spaced, parallel discs mounted on a rotating shaft which is supported just above the surface of the waste water. Microorganisms grow on the surface of the discs where biological degradation of the wastewater pollutants takes place.
The rotating packs of disks (known as the media) are contained in a tank or trough and rotate at between 2 and 5 revolutions per minute. Commonly used plastics for the media are polythene, PVC and expanded polystyrene. The shaft is aligned with the flow of wastewater so that the discs rotate at right angles to the flow with several packs usually combined to make up a treatment train. About 40% of the disc area is immersed in the wastewater.
Biofilms, which are biological growths that become attached to the discs, assimilate the organic materials in the wastewater. Aeration is provided by the rotating action, which exposes the media to the air after contacting them with the wastewater, facilitating the degradation of the pollutants being removed. The degree of wastewater treatment is related to the amount of media surface area and the quality and volume of the inflowing wastewater.
from here, the liquid mixture, composed of solids with microorganisms and water, is sent to the clarifier. here the solids settle to the bottom where some of the material is sent to the solids handling process.
- Final Treatment
Wastewater that remains is disinfected to kill harmful microorganisms before being released into receiving waters. Although, there are many methods available to kill these microorganisms, chlorination will be used in this particular treatment.
From the data given by the __________, the total volume of wastewater generated everyday at the Palao Market is 37.16 cubic meter.
According to the test result of the Department of Chemistry, MSU-IIT, the total suspended solids (TSS) of the wastewater from Palao Market is 1, 595.50 mg/L and its corresponding total dissolved solids (TDS) is 2, 060.00 mg/L. These constitute the pollutants in the wastewater, which then can be summed up to 3.655.50 mg/L of wastes present in the water.
Also, sample of the wastewater underwent Biological Oxygen Demand (BOD) analysis for five days, that is BOD5,and the results showed that the wastewater contains 6, 000 mg/L.
- Material Balance at the Sedimentation tank
Sedimentation is the process where wastewater flows into a primary settling tank where it is held for 2.5 hours. This allows solid particles to settle at the bottom of the tank. Consequently, flocculants such as FeCl2 and Lime are added.
With a basis of one day of operation, the mass of solids, dissolved and suspended, in the wastewater entering is
The mass of the flocculants needed for this process is given by ______.
After acquiring the amount of FeCl2, the amount of Alum needed can then be solved,
Therefore, the mass of the sludge produced in the sedimentation process is,
That is to say, the sludge created during the process is the 75% of the total suspended solids and 6% of the total dissolved solids as well as the amount of lime and FeCl2 added during the flocculation.
Since only 75% and 6% of the TSS and TDS, respectively, were able to remove during the primary treatment, thus, it is necessary to say that the remaining solids still goes out and flow through the secondary treatment and the solids going out is actually,
As for the BOD balance around the sedimentation tank,
The BOD that goes out with the sludge is 55% of the total BOD of the untreated wastewater according to ____. That is,
Therefore the remaining BOD that flows through the secondary treatment is
The size of the settling tank is actually a cylindrical tank having a height and diameter of (assuming height=diameter),
- Mass Balance around the Rotating Biological Contactor and the Clarifier
wastewater from sedimentation tank
wastewater to filter
The secondary treatment is composed of the rotating biological reactor (RBC) and the clarifier. since the secondary treatment is actually a biological treatment of the wastewater, then it is safe to assume that the BOD balance is the one necessary for this particular treatment.
According to ______, the efficiency of a RBC is 85%. meaning, t85% of the original BOD of the incoming stream is flushed out of the process with the sludge, then,
Having the solid balance within the secondary treatment,
The sludge that will be formed is
As a result, the solids that will remain after the clarifier is
- Material Balance around the Final Treatment
Since the amount of the remaining solids is so low, it is then safe to believe that all of the solids will be discharged out of the main process or after the filtration. This amount of water per time is then contacted with chlorine (chlorination) in order to disinfect the treated wastewater. Since it is said before that 99% of wastewater is water, then this amount will then be the volume of the treated wastewater ready for discharge or reuse.