Sewage sludge recycling—an alternative to digestion and incineration

Improving the efficiency of activated carbon beds in water and waste treatment Stringent emission regulations on waste water require that some liquid effluents be polishd via activated charcoal beds before being discharged into the environment. This process is extremely expensive and may not be completely necessary. For this reason Applikon Analyzers has introduced a method of increasing the efficency of the charcoal beds and reducing the costs of online monitoring and control. Continuous on-line control measurement of the Total Carbon/Total Organic Carbon (TC/TOC) provides a clear indication of the level of contaminants present. The results are used to activate a bypass valve when the beds are not required, which in turn maximises the service life and cleaning capacity of the charcoal bed.

An on-line TC/TOC analyser installed to monitor the inlet levels (ranging from 0 to 1000ppm) will protect the expensive charcoal bed by switching the flow via a bypass when polishing is not required. It is also able to switch the flow to a holding tank or pond should an amount of potential bed destroying effluent be detected due to upstream equipment failure or spillage. The outlet is also monitored to ensure the continued performance of the bed and to signal the time for bed regeneration. The analysers use an ultraviolet/persulphate oxidation system, that converts all dissolved carbon into COz. The quantity of gas is measured by the Non-dispersive Infrared (NDIR) CO2 detection system and automatic compensation for ageing and impurity

Sewage sludge recycling -an digestion and incineration A second Simon-N-Viro sewage sludge recycling plant is to be built in the UK. Simon-Hartely, a member of the Simon Group, will build the plant at the Coleshill water treatment works of Severn Trent. The Coleshill installation, similar in size to the first one that opened last year, at Horsham for Southern Water, will be operational during the first quarter of 1991. It will cost 2250 000 and will

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alternative to

be able to recycle the sewage sludge from a population of 100 000 into Simon-N-Viro soil. This is a dry, granular, storable, odourless material that can be used as a soil conditioner, for landscaping or for landfill without environmental damage; any heavy metal content being locked in chemically. The commissioning of a second Simon-N-Viro installation demonstrates that the recycling of sewage sludge is

Filtration systems for recycling extruders Two filtration systems for

recycling extruders have been introduced that are claimed to overcome problems of production interruptions and variations in product quality that may be encountered with slide-plate screen-changers. The fully automatic separator is designed for applications where contamination levels are high and impurities are coarse and hard. It incoraccumulation ensures continporates a permanent screen uous long term stable monplate with 0.5mm drilled itoring. The analysers are easy holes mounted in the meltto install and have been flow channel. constructed to withstand proA wheel, mounted eccentrlccess brine and corrosive samally to the extrusion axis, ples. With a wide detection scrapes away the contaminarange and fast response they tion on the breaker plate and provide a cost-effective monbrings it to the exterior of itoring system. melt channel between the ribs of the wheel, where it is ejected. Applikon Analyzers (UK), AlexanThe unit is controlled by der House, Station Road, Alderpressure of the melt, that is, shot, Hanis GUl7 7SQ (UK) the speed of rotation is controlled by the level of contamination. Extrusion takes firmly on the agenda for the place at constant pressure UK Water Industry and that without interruption. there are alternatives to diThe second stage of filtragestion and incineration. tion, to remove smaller partiIn the United States the Ncles, can be accomplished with Viro process recently received a self-purging continuous the US Environmental F’rotecscreen-changer called the Retion Agency’s 1990 award for Lvcling Filter. This unit, which Technology Development in can be fitted downstream of Beneficial Sewage Sludge use. the Separator, also operates In the Simon-N-Viro process, with a filter wheel fitted which takes less than seven eccentrically to the extrusion days to complete, a quality axis. The wheel contains a controlled combination of number of breaker plates alkaline products is mixed fitted with screen-packs, with dewatered sewage which rotate in and out of sludge in specially designed the melt stream. The speed of facilities. rotation is determined by the The ensuing chemical reaclevel of contamination. tions produce heat to Ml the An important feature is a pathogens in the sludge, conbackflush system in which a vert any heavy metals that melt channel upstream of the may be present into inactive filter wheel admits a small hydrates, reduce the moisture amount of filtered polymer content further and reduce and is fed back to the extruacidity. The nutrients and der. Behind the filter wheel, trace elements already in the the channel opens out into a sludge are unaffected and so slot shape. When the filter are available for use in the wheel indexes one step, a end product. valve in front of the unit opens and closes, allowing Simon-Hartley, Stoke-on-Trent, the melt in the channel to Staftordshire ST4 7BH (UK) surge over the screen-pack from behind, lifting off the contamination and discharging it at the front of the Converting sewage slu@e into a unit. A screen-pack can be storable,dry, granular,odorcrless used 80 times. andenvinmm~&~Jly acceptable material for use in agnL&ural or Gneuss Inc., Langhorne, landscapinsapplhtims. Pennsylvania USA May/June 1991

Filtration& Separation