Turbidity is caused by a large amount of small suspended materials. These materials are easily stirred up in water and are very slow to settle. They can be caused by the growth of algae and plankton, sediment and particles found in runoff from land in stormwater, disturbance due to storms, etc. High levels of turbidity interfere with the water treatment process and also are an indicator that a portion of the process is not working properly. The level of turbidity can be affected by the processes of raw water screening, presedimentation, coagulation, flocculation, sedimentation, and filtration. Although the intake screens have no effect on turbidity, the location of the raw water intake can have a significant effect on the amount of turbidity entering the water treatment system. Presedimentation helps to remove silt and other fine suspended solids. The lower the velocity flow of the water, the greater the sedimentation. Since the particles carry electrical charges, they can be brought together if a material of the opposite electrical charge is introduced into the water. Coagulation by itself will not reduce turbidity but may increase it. The flocculation of the larger particles helps reduce the turbidity. Once again, detention time is very important. Sedimentation and clarification can remove 50-90% of the suspended solids. Filtration if working properly can reduce the turbidity to below the acceptable safe drinking water standards. Membrane systems work the best at reducing turbidity.
Best Practices for Drinking Water Treatment Facilities
• The water treatment plant location and its conduits, basins, other structures, storage areas, and distribution systems must be secure against the infiltration of sewage, surface contaminants, and runoff from surrounding lands.
• The water treatment plant must have special extra reserve power sources and pumping equipment in the event that the initial sources are made inoperable. They must be able to be switched in to operation quickly.
• Filter washings and other types of wastes must be removed safely and quickly to points of disposal on a regular basis, except in extreme weather where adequate storage should be available to be used until the extreme weather passes.
• Separate reservoirs are used for presettling of contaminants prior to water treatment and a finished reservoir which must be covered when the water is ready for distribution to the community.
• Develop a disinfection profile for the facility by keeping a log of G. lamblia and virus inactivation for at least a 12-month period of time and the amount and type of disinfectant used as well as the time of application. This will help establish the guidelines for disinfecting the water to destroy these organisms and if additional treatment is necessary.
• The maximum contaminant level goal for the protozoan Cryptosporidium is zero and since it is chlorine-resistant, the membrane processes using micro- and ultrafiltration as well as the use of ozone or the second-best disinfectant, chlorine dioxide, will reduce the potential for contamination to its lowest level.
• Continuously monitor turbidity in the effluent from the individual filters to determine the level of performance of that filter and whether or not it needs cleaning, maintenance, or replacement.
• All filter backwash water, thickener supernatant, or liquids from dewatering must be recycled to remove contaminants from the effluent.
• The water is tested for 83 different contaminants including volatile organic compounds, synthetic organic compounds, inorganic compounds, and microorganisms. If the water does not meet state and federal standards, it has to be reprocessed and a determination needs to be made of why, after treatment, the water was still not considered to be of drinking water quality.
• All water should be fluoridated before it can be utilized for human consumption.
• All water treatment plant operators must be properly trained and licensed by the appropriate authorizing authority. They must take continuing education courses either yearly or every 2 years to be recertified before being able to be relicensed.
• All water treatment plant equipment must be in excellent operating condition and all problems, breakdowns, incidents, and accidents must be put on a permanent log along with appropriate numbers of samples of the water depending on the size of the plant.
• Graphs must be made of water flow, turbidity, dosage rates of chemicals, etc. and be evaluated monthly by the supervisor and cosigned by him/her.
• Raw water variability by quality or quantity must be charted, problems determined, reports made to supervising personnel, and problems corrected as quickly as possible.
• Incidents of no disinfectant present in the finished water or varying amounts must be brought immediately to the attention of the supervisor and all necessary precautions taken to avoid the potential for creating a health risk.
• All equipment and standby equipment must be evaluated periodically and kept in proper operating condition for immediate use.
• All hazardous chemicals on site must be secured in a properly ventilated storage area and used only by individuals appropriately trained and if necessary using personal protective equipment.
• There should be an immediately usable communication systems and a properly tested and operating back-up system if necessary in the event of an emergency.
• Cleaning and maintenance of all facilities is extremely urgent to prevent contamination of the water.
• Develop a specific safety plan for each facility, communicate its contents to all people working, and enforce all measures necessary prevent injury or illness.
• Conduct sanitary surveys using appropriately qualified professionals on a regular basis to determine the potential for problems in the water treatment plant and the water distribution system before they occur.
(See endnotes 22, 23, 24, 25, 26, 28)
After the potable water goes through the various phases of the drinking water treatment plant, the water is then disinfected to ensure that all disease-causing organisms or other pathogens are destroyed. The disinfectants being used are chloramine, chlorine, and chlorine dioxide.