sand drying beds

reedbed technology

reedbed technology

The proper utilization and disposal of sludge is one of the most critical issues facing wastewater treatment plants today. Nearly all wastewater treatment plant operators face the problem of storing and disposing biosolids. Landfill costs are skyrocketing; incineration permits are expensive and difficult to obtain; and land application is limited by availability of permitted land. However, constructed wetland technology such as reed beds provide long-term storage and volume reduction of biosolids to mitigate these concerns. Widely used throughout Europe, Asia, and Australia, and in more than 50 locations in the United States, reedbed technology features low construction costs and minimal day-to-day operation and maintenance costs. Much interest is also being shown in Canada for their use. The system reduces water content, minimizes solids, and provides sufficient storage time to stabilize biosolids prior to disposal.

The solution is slowly gaining acceptance in Maine is sludge reed beds. Phragmites are only one of natures age old processes which have been adapted by man in the battle against pollution. They were first used years ago in Europe in an attempt to deal with iron oxide sludges.

Reed beds use common reed plants (phragnmites communis, a second cousin of the common marsh plant) to dewater solids in a confined area. The beds can be any shape to accommodate existing land conditions and areas. Specially designed ponds with underdrains covered by a sand and gravel mixture are constructed and filled with reed plants. Modified sludge drying beds also work well and are an ideal retrofit. They already have side walls, layers of sand and gravel, an underdrain system which collects and carries away filtrate, and an impervious membrane liner. Solids are pumped into the reed beds. Dewatering occurs through evaporation, plant transpiration, and decantation. Decanted water seeps through the bottom of the bed and through the layers of sand and gravel into the underdrains, traveling back to the wastewater treatment plant for secondary treatment. During dewatering the solids change from liquid to "cake." Six inches of solids and water will compress to a half inch of solid cake. The cake is left in the bed and the process is repeated.

The reeds are planted one foot on center throughout the bed. Aerobically stabilized sludge is typically applied uniformly through a grid-perforated tile. Sludges must be well stabilized, 60% volatilized or less to be used successfully with reed beds. Optimum application rates range between two and four percent solids. While plants are young they should be watered with plant effluent. After they are established, they can be fed heavier sludge mixtures. Loading rates in Maine are typically about 45 gallons per square foot per year for well-established beds.

The phragmite is one of the most widespread flowering plants in the world. It is a tough adaptable plant, which can grow in polluted waters and find sustenance in sludge. This reed has a voracious appetite for water. The plant is tolerant to low oxygen levels and to waterlogged conditions. The reeds hold themselves in the soil through roots and rhizomes, an intricate network of underground stems. New plants in turn will sprout from these stems. These rapidly growing roots provide air passages through the sludge which in turn provide a host area for many biological communities to develop and continue to mineralize the sludge.

Reed beds perform three basic functions: (1) dewater the sludge, (2) transform it into mineral and humus like components, and (3) store sludge for a number of years. Dewatering is accomplished through evaporation (as in a normal sludge drying bed operation); transpiration through the plants root stem, and leaf structure; and filtration through the bed's sand and gravel layers and the plant's root system. Leachate is channeled back to the treatment plant through the underdrain.

Researchers recommend the installation of multiple beds to handle emergencies and downtime due to cleaning. Beds may be out of service for up to a year while root stalks grow new tops after cleaning. The top level of sand and material removed during clean out is similar in pathogen content to composted sludge and can be used in the same way. Many beds have gone eight to ten years without having to be cleaned out.

Sludge reed beds are a significant improvement over existing drying beds. Sludge can be dewatered and converted into biomass and a low-grade compost without chemical addition or energy. They have lengthy turnover time and are capable of reducing sludge volumes by up to 95% over time.

sludge drying bed | sanitation engineering | britannica

sludge drying bed | sanitation engineering | britannica

Sludge-drying beds provide the simplest method of dewatering. A digested sludge slurry is spread on an open bed of sand and allowed to remain until dry. Drying takes place by a combination of evaporation and gravity drainage through the sand. A piping network built under

wastewater treatment | process, history, importance, systems, & technologies | britannica

wastewater treatment | process, history, importance, systems, & technologies | britannica

Wastewater treatment, also called sewage treatment, the removal of impurities from wastewater, or sewage, before it reaches aquifers or natural bodies of water such as rivers, lakes, estuaries, and oceans. Since pure water is not found in nature (i.e., outside chemical laboratories), any distinction between clean water and polluted water depends on the type and concentration of impurities found in the water as well as on its intended use. In broad terms, water is said to be polluted when it contains enough impurities to make it unfit for a particular use, such as drinking, swimming, or fishing. Although water quality is affected by natural conditions, the word pollution usually implies human activity as the source of contamination. Water pollution, therefore, is caused primarily by the drainage of contaminated wastewater into surface water or groundwater, and wastewater treatment is a major element of water pollution control.

Wastewater is the polluted form of water generated from rainwater runoff and human activities. It is also called sewage. It is typically categorized by the manner in which it is generatedspecifically, as domestic sewage, industrial sewage, or storm sewage (stormwater).

Wastewater contains a wide range of contaminants. The quantities and concentrations of these substances depend upon their source. Pollutants are typically categorized as physical, chemical, and biological. Common pollutants include complex organic materials, nitrogen- and phosphorus-rich compounds, and pathogenic organisms (bacteria, viruses, and protozoa). Synthetic organic chemicals, inorganic chemicals, microplastics, sediments, radioactive substances, oil, heat, and many other pollutants may also be present in wastewater.

Sewage treatment facilities use physical, chemical, and biological processes for water purification. The processes used in these facilities are also categorized as preliminary, primary, secondary, and tertiary. Preliminary and primary stages remove rags and suspended solids. Secondary processes mainly remove suspended and dissolved organics. Tertiary methods achieve nutrient removal and further polishing of wastewater. Disinfection, the final step, destroys remaining pathogens. The waste sludge generated during treatment is separately stabilized, dewatered, and sent to landfills or used in land applications.

Wastewater is a complex blend of metals, nutrients, and specialized chemicals. Recovery of these valuable materials can help to offset a communitys growing demands for natural resources. Resource recovery concepts are evolving, and researchers are investigating and developing numerous technologies. Reclamation and reuse of treated water for irrigation, groundwater recharge, or recreational purposes are particular areas of focus.

Many ancient cities had drainage systems, but they were primarily intended to carry rainwater away from roofs and pavements. A notable example is the drainage system of ancient Rome. It included many surface conduits that were connected to a large vaulted channel called the Cloaca Maxima (Great Sewer), which carried drainage water to the Tiber River. Built of stone and on a grand scale, the Cloaca Maxima is one of the oldest existing monuments of Roman engineering.

There was little progress in urban drainage or sewerage during the Middle Ages. Privy vaults and cesspools were used, but most wastes were simply dumped into gutters to be flushed through the drains by floods. Toilets (water closets) were installed in houses in the early 19th century, but they were usually connected to cesspools, not to sewers. In densely populated areas, local conditions soon became intolerable because the cesspools were seldom emptied and frequently overflowed. The threat to public health became apparent. In England in the middle of the 19th century, outbreaks of cholera were traced directly to well-water supplies contaminated with human waste from privy vaults and cesspools. It soon became necessary for all water closets in the larger towns to be connected directly to the storm sewers. This transferred sewage from the ground near houses to nearby bodies of water. Thus, a new problem emerged: surface water pollution.

It used to be said that the solution to pollution is dilution. When small amounts of sewage are discharged into a flowing body of water, a natural process of stream self-purification occurs. Densely populated communities generate such large quantities of sewage, however, that dilution alone does not prevent pollution. This makes it necessary to treat or purify wastewater to some degree before disposal.

The construction of centralized sewage treatment plants began in the late 19th and early 20th centuries, principally in the United Kingdom and the United States. Instead of discharging sewage directly into a nearby body of water, it was first passed through a combination of physical, biological, and chemical processes that removed some or most of the pollutants. Also beginning in the 1900s, new sewage-collection systems were designed to separate storm water from domestic wastewater, so that treatment plants did not become overloaded during periods of wet weather.

After the middle of the 20th century, increasing public concern for environmental quality led to broader and more stringent regulation of wastewater disposal practices. Higher levels of treatment were required. For example, pretreatment of industrial wastewater, with the aim of preventing toxic chemicals from interfering with the biological processes used at sewage treatment plants, often became a necessity. In fact, wastewater treatment technology advanced to the point where it became possible to remove virtually all pollutants from sewage. This was so expensive, however, that such high levels of treatment were not usually justified.

Wastewater treatment plants became large, complex facilities that required considerable amounts of energy for their operation. After the rise of oil prices in the 1970s, concern for energy conservation became a more important factor in the design of new pollution control systems. Consequently, land disposal and subsurface disposal of sewage began to receive increased attention where feasible. Such low-tech pollution control methods not only might help to conserve energy but also might serve to recycle nutrients and replenish groundwater supplies.

merit filter the future of dewatering

merit filter the future of dewatering

Many years of developing and testing various dewatering devices for efficiency and reliability ends right here. The Merit Filter Media sludge dewatering system now offers the best financial alternative to both costly mechanical dewatering and obsolete, inefficient sand drying beds. Best of all, Merit Filter Media can be retrofitted to any existing sand drying bed simply and inexpensively. The new Merit Filter Media is the improved dewatering system.

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