What is wastewater? And why should we care about it?
What is sewage? Sewage is generated by residential, institutional, and commercial and industrial establishments. It includes household waste liquid from toilets, baths, showers, kitchens, sinks and so forth that is disposed of via sewers.
Separating sewage from drinking water In cities as late as the 1800s, human waste was collected from the privy and dumped in streets or nearby cesspool. This waste eventually drained to the local water source where it polluted drinking water.
Population Explosion in late 1800s US population grew from 5 million to 75 million. In 1820 less than 5% of population lived in cities, by 1860 it had risen to 16% and by 1880 it had risen to 22.5%. As cities started to evolve, population density increased. It was becoming more likely that one man’s sewage could become another man’s drinking water.
Mid 1800s Solution: Limit It! Growing city populations were generating too much waster water. In some growing cities, ordinances were put in place to limit the amount of wastewater people generated. E.g. 1844 Boston – a bath required a doctor’s note!
Connection made between disease and polluted drinking water. Prior to the mid 1800s, people did not understand the connection. Sewage was seen more as a nuisance than a health hazard. Suspicion’s arose that proximity to sewage caused disease and people were motivated to move it away from the cities.
London, Cholera and Broad St. Pump Cholera outbreak in 1854 in London People had suspected cholera was transmitted through the air. Dr. John Snow made a famous map of the neighborhood, marking all cases on the map. Incidences of disease centered around the Broad Street Pump. Dr. Snow concluded that cholera was transmitted via tainted water. Pump was disabled and cholera subsided.
U.S. Cities Developed Water Carriage Systems U.S. Cities were influenced by developments in Europe. Cities were piping in water for water supply of growing city population. Necessary for adequate water supply and fire fighting. Availability of piped in water resulted in implementation of modern plumbing fixtures (indoor toilets!) Piped-in water supply made water carriage sewer systems viable. A centralized water-carriage system was seen as the only viable alternative to manage the growing amount of wastewater.
Origins of CSS (Combined Sewage Systems) CSS = sewage + storm water 1 st CSS system in Hamburg, Germany In the late 1850s, cities such as Chicago and Boston developed CSSs Early CSSs simply discharged the effluent to the nearest body of water. Sewers were built both below ground as underground conduits and above ground as open channels. Typically they ran along the center of a street or the sides of a street.
Pros/cons of CSS PROS Combined systems mix storm water and waste water, so waste water just added in to existing flow. In some cities infrastructure was already in place. CONS In a combined system there is tremendous variation in flow due to storms. Sewage overflow can occur when volume is too high.
SSS (Separate Sewer System) Advocated by some First U.S. SSS built in 1875 in Lenox, MA New small diameter clay pipes made it possible. SSS built in 1880 in Memphis, TN and is credited in reducing incidences of yellow fever (mosquito borne disease).
Pros/Cons of SSS PROS Less volume to treat Flow was more consistent (not affected by storms) CONS Infrastructure needed to be built.
1900s - Gradual Shift to SSS CSS vs SSS - no sanitary advantage seen. Cities that were established after turn of century usually implemented SSS. When cities began treating waste water there was less to treat in a SSS. Population growing generated too much effluent for CSS infrastructure Nature of wastewater was changing
Factors Affecting CSS vs. SSS Was there an existing sewer system serving the population in the area; and if so, was it a separate, combined, or paritally separate system? Was there a waterway nearby and what was the capacity of the waterway to dilute wastewater? Was pumping a possible requirement?
Philosophy on Wastewater Treatment in 1903 “…it is often more equitable to all concerned for an upper riparian city to discharge its sewage into a stream and a lower riparian city to filter the water of the same stream for a domestic supply, than for the former city to be forced to put in wastewater treatment works.” -- published in 1903 Engineering Record
When did we start treating wastewater? Prior to turn of the century, bodies of water were able to dilute the population’s wastewater sufficiently. What motivated us to start treating wastewater? Progressive movement in early 1900s – value of resource conservation. New laws protecting water quality. Stricter enforcement – ruling in favor of downstream cities. Pressure from business and public health groups.
How do we get sewage to the waste water treatment plants. How sewage gets to the treatment plant. ~ pipes must drop ~ periodic lifts going inside of sewer pipes would be deadly??
How does waste water treatment work? Preliminary Treatment Primary Treatment Secondary Treatment Solids Handling
Preliminary Treatment Sewage moves through large screens where solids are removed. Water is slowed to allow more solids to drop to bottom, such as sand, grit, etc… These solids are sent to a landfill.
Primary Treatment Settling tanks hold wastewater for several hours to allow suspended solids to settle to the bottom. Surface skimmers remove grease and oil.
Secondary Treatment Converting dissolved solids to suspended solids that can be removed via aerobic digestion. Seed with good bacteria that feed on harmful organic matter. Add oxygen to help speed up the process. Suspended solids are allowed to settle and are then removed. Chlorination to kill remaining solids that cause disease De-chlorinate to remove chlorine that is toxic. Effluent is released to the waterways.
Solid Handling Solids that have settled out in primary and secondary sedimentation process, called “biosolids” or “sludge.” As much water as possible is removed from sludge via sludge cooking, spinning, chemicals or pressurization. But what to do with the remaining sludge?
Solid Handling Old method for dealing with sludge: burn it and take to landfill. New method for dealing with sludge: anaerobic digestion. Sludge is pumped into digesters that process the solid material through bacterial decomposition that renders a form of stabilized sludge or bio-solid which can be used as fertilizer and methane produced for energy. Dubuque, IA example "In 2005, the Lawrence Berkeley National Laboratory determined that the energy potential in municipal wastewater in the United States is estimated to be as high as 7.20 million kilowatt hours of electricity. This endless supply of energy is greater than the production of the Hoover Dam and Glen Canyon Dam combined.”” Melvin W. Cook, Founder, CTO of Filtration Dynamics
Video: Tour of Wastewater Treatment Plant http://vimeo.com/1973831
History of Waste Water Treatment 1850s to present day
Late 1800s: Initial Efforts TRENDS: awareness and control of impacts of sewage discharge on receiving waters through standards, regulation, and simple treatment (probably now called “primary”) 1887, first biological treatment, an intermittent sand filter, was installed in Medford, Mass. 1886, Standards for discharge loading and treatment developed at Lawrence, Mass experiment station and for Chicago, IL (Rudolph Hering) 1899, first federal regulation of sewage, Rivers and Harbors Appropriations (“Refuse Act”) prohibited discharge of solids to navigational waters without permit from US Army Corps of Engineers Pit privies and open ditches replaced by buried sewers: sewered population increased from 1 million in 1860 to 25 million by 1900.
Early 1900s: TREND: population growth and sewer construction 1900-1930s Early 1900s, 1 million people served by 60 sewage treatment plants for removal of settling and floating solids. Population using sewers increases at same rate as total population Construction of a sewage treatment plant in early 1900s near Cleveland.
Early 1900s TREND: development of secondary (biological treatment) 1901: first trickling filter operated in Madison, WI 1909, first Imhoff tank (solids settling) 1914, first liquid chlorination process for effluent disinfection 1916, first activated sludge plant, San Marcos, TX
Mid 1900s TREND: protection of receiving water quality. 1920 – 1940’s: Wastewater treatment linked with importance of dissolved oxygen to aquatic life, aesthetic properties of surface waters (odor, color, solids), measurement of organic matter in sewage as biological oxygen demand (BOD) 1944 Steeter Phelps DO sag curve model for streams to predict BOD assimilation capacity Secondary treatment processes to remove BOD
Early/Mid 1900s: Sludge Increased wastewater treatment meant increased residuals (sludge). Heated sludge digesters and use of gas. 1921: mechanical dewatering of sludge in vacuum filters and centrifuges, Milwaukee, WI. Early 1930’s: sludge drying and incineration in Chicago.
Mid 1900s: Clean Water Regulations TREND: New Regulation and Government Grants 1948: Federal Water Pollution Control Act. Primarily for provision of federal funds for water quality surveys and construction of collection and treatment plants. 1966 (Clean Water Restoration Act) extended federal grants for plant construction. 1960 MILESTONE: 50% of US population had access to some form of wastewater treatment.
Mid/Late 1900s: Advancements TREND: Treatment process advancements to improve receiving water quality Nutrient (nitrogen and phosphorus) removal (eutrophication control) Use of chemical conditioners (polymers, polyelectrolytes), dissolved air flotation for enhanced solids separation and thickening New process configurations: high rate activated sludge processes, high purity oxygen, sequencing batch reactors, high rate trickling filters and hybrid trickling filter-activated sludge processes, membrane bioreactors Improved sludge digesters: high temperature processes Effluent disinfection
Late 1900s: More Regulations TREND: Regulation 1972 Federal Water Pollution Control Act Amendments (PL 92- 500) amended 1977 (Clean Water Act. CWA summary Water Quality Standards for receiving waters (based on designated uses and related human health and aquatic life criteria) Antidegradation policy with ambient monitoring If WQS not met: plan (strategies and controls) to improve impaired waters using Total Maximum Daily Load (TMDL) approach. Implementation: POINT SOURCES. National Pollutant Discharge Elimination System (NPDES) PERMIT PROGRAM o Control of toxics, Industrial pretreatment of Sludge (Biosolids) disposal Non- point sources (section 319) Section 404 (Wetlands protection) State Revolving Funds
Emerging Trends in Sewage Treatment TREND: Wastewater Reuse Non-potable, separate distribution TREND: Energy Recovery of energy (biofuels, co-generation, fertilizer) Conservation of energy (aeration, pumping, mechanical solids processing, heating, embedded materials) CO2 caps? TREND: Decentralized wastewater management in developing urban fringe areas.