The winter snow pack on the mountain sides fills the alpine lakes. One of these, Lake Tahoe, overflows its pristine water into the Truckee River. The river winds down to the valleys below, to the cities of Reno and Sparks. Canals and ditches fed by the Truckee River irrigate agricultural areas. The residents of the valleys know the importance of this natural resource in the high desert. Each drop is managed for its best utility. The area has prospered, commerce has developed, and thousands of people have come to marvel at this scenic wonderland in the mountains. Many who come to visit become residents. The Truckee Meadows is one of the fastest growing metropolitan centers in the nation. Water conservation practices have secured a stable economic base during the lean water years. Water reuse has been a major issue in the cities of Reno and Sparks and it will become a greater issue in the future as the availability of water decreases.
Water reclamation is also important to the cities\\' downstream neighbors. In the past, technology has limited the recovery of high quality water. However, the Truckee Meadows Water Reclamation Facility (TMWRF) has taken steps to provide a source of clean water for these downstream users.
A Bit of History
Sewage treatment in the Reno/Sparks area was originally accomplished by discharging waste to the natural streams. As the population grew, the stream lost its ability to cleanse the water of its wastes. Eventually, city inhabitants found that if a common collection point in each of the cities could be established, treatment plants could be built to treat the wastes. As a result, primary treatment ponds were incorporated to provide some treatment before discharge into the streams. The biological fauna in the stream bed assimilated the contaminants as nutrients essential to their growth. This mode of treatment was inexpensive and effective, until the population became too large.
In the 1940\\'s, the Truckee River began to lose its ability to service the community as a natural reclamation source. Trickling filters were added in series with the primary sedimentation ponds to provide a higher degree of treatment. The combination of the primary ponds and trickling filters removed a greater amount of the wastes and helped the Truckee River recover its natural treatment ability.
Commerce continued to flourish through the next 20 years, and the population of the cities doubled. The treatment plant was expanded to meet the needs of the growing community. Activated sludge treatment was implemented which produced a high quality effluent.
In the following decades, the cities of Reno and Sparks assumed an even greater responsibility for maintaining a clean environment by incorporating phosphorus removal to prevent eutrophication and protect the quality of the Truckee River. Wildlife experts lauded the approach and are convinced that these efforts will pay off in re-establishing the endemic fish populations in the Truckee: the Lahonton Cutthroat Trout and the Pyramid Lake Cui Ui. The city\\'s goal will be attained when the final features of their advanced wastewater plant are completed. When finished, the water from the TMWRF will approach the clarity and chemical purity of the river itself.
The Truckee Meadows Water Reclamation Facility is located to the east of the Truckee Meadows and has a sophisticated operation, which requires the expertise of a group of highly trained personnel.
How it Works
Raw sewage enters the treatment facility through the sanitary sewer system. Large objects and grit which may damage pumps or other equipment are screened out. The solids collected in the preliminary treatment process are dewatered and hauled away to a landfill. In the primary treatment process, primary sedimentation tanks use gravity to settle large solids from the waste stream. The removed solids are pumped to anaerobic sludge digesters for further processing, while the wastewater continues to the biological treatment. Aeration basins are the heart of the biological treatment process. Oxygen, is supplied by aeration, which ensures a proper environment for microorganisms. The microorganisms group together and settle to the bottom of the secondary sedimentation tanks. Some of these solids are then returned to the aeration basin as seed organisms to help break down the fresh incoming sewage. Organisms from the secondary sedimentation tanks may also be pumped to anaerobic sludge digesters, or to the phosphorus removal tanks.
In the phosphorus removal tanks, organisms loaded with phosphorus collected from the wastewater are deprived of oxygen for a long time. The oxygen deprivation causes the organisms to become stressed and phosphorus is released from the organism cells into the waste stream. Stripped of phosphorus, bacteria are returned to the aeration basin where they consume more nutrients than they would normally need. The cycle is then repeated. The overflow from the phosphorus tanks is saturated with a high level of phosphorus and goes on to chemical treatment. In the chemical treatment process, lime is added to the phosphorus saturated stream which is settled in separate clarifier tanks. This lime phosphate sludge is then removed and pumped to anaerobic digesters.
All of the solids, or sludges, removed from various parts of the waste treatment process are sent to the anaerobic sludge digesters. Methane gas is produced in this process, which is captured and used to run plant equipment. By utilizing this gas, electrical costs for running the treatment facility are kept to a minimum. Digested sludge is then sent on to the sludge drying process. Sludge drying, or dewatering, is accomplished by large centrifuge units that separate the solids from the liquid with the help of chemicals. Sludge may be used as a soil conditioner, adding phosphorus and other nutrients to barren soils.
Wastewater also flows to the nitrification pump station for further treatment. The purpose of nitrification is to convert ammonia, which can be toxic to fish, into nitrate. In the nitrification process, the wastewater is spread over a column of synthetic media where microorganisms are grown. These organisms oxidize the ammonia compounds to nitrate. These nitrates are removed in the denitrification process. In the denitrification process, nitrates, which also may be hazardous to aquatic life, are reduced biologically to harmless nitrogen gas, which is released into the atmosphere. Wastewater then enters the chemical mixing facility for further treatment. In the chemical mixing tank, such things as aluminum sulfate (alum), ferric chloride, or polyelectrolites may be added in order to maintain proper pH levels or serve as a pre-conditioning step prior to filtration. In the filtration process, the water stream is passed through filter media, which will remove any remaining particulate matter left in the waste stream. After filtration, the wastewater enters the chlorination basin where chlorine is added in order to kill any remaining pathogenic organisms. Sulfur dioxide is then added to neutralize chlorine before effluent leaves the treatment plant. This neutralization process protects fish and other aquatic life from chlorine toxicity. After leaving the chlorine removal tank, the water is oxygenated and delivered into the receiving stream. The effluent is discharged to Steamboat Creek and ultimately to the Truckee River.
Today
Now and in the future, the citizens of the twin cities can be proud of preserving water quality. Downstream users can continue to look forward to receiving clean Truckee River water in this age of responsibility. In the midst of economic development and population growth, the river system will benefit from the greatest effort ever instituted to preserve its pristine beauty.
