Water Journal : Water Journal December 2011
water DECEMBER 2011 77 small wastewater systems Summary Operating experience at municipal wastewater treatment plants (WWTPs) in Morocco was used to develop design criteria and operating procedures for the construction of two new WWTPs in Shobak and North Shouneh, Jordan, to treat septage from small communities to water reuse standards. The WWTPs use an anaerobic/settling digestion tank, facultative lagoons, intermittent or recirculating sand filters, and reed beds to remove solids, carbon, nitrogen and pathogens. The facilities are sustainable in that they minimise the use of complex mechanical and electrical equipment, do not require chemicals or high electrical demands, and produce beneficial products for the communities, which include irrigation water, reeds and dried biosolids that can be used as a soil amendment and, as such, may be suitable for consideration in similar climates in Australia, dependent on local regulations. Introduction Rural areas in developing countries are best served by treatment facilities that do not require complex mechanical processes and that minimise power costs, chemical usage and operational requirements. In addition, treatment facilities in arid areas that choose to reuse the treated effluent must reliably provide a high level of treatment in order to protect public health. Reuse standards for nitrogen can prove particularly challenging to achieve without complex systems. This paper presents experience with the design and operation of treatment facilities in Morocco and Jordan that are using relatively simple lagoon and fixed film processes to achieve ammonia and nitrogen removal to meet various reuse standards. The treatment plants presented include Ben Sergao and Drarga (Morocco), and Shobak and North Shouneh (Jordan). The experience gained at these facilities provides design and operational guidance relevant to treating both high-strength domestic wastewater and septage to achieve nitrogen limits to meet reuse standards. General Description of Treatment Processes Solids and carbon removal Manually cleaned coarse screens are used at all facilities for preliminary treatment. For facilities treating moderate to high- strength domestic wastewater, anaerobic lagoons provide the initial treatment step for solids and carbon removal. For facilities treating septage, anaerobic/ settling digestion tanks are used for solids removal and digestion. The initial treatment units are covered to maintain warmer temperatures and minimise odours. Although methane collection from these lagoons was evaluated and included in the treatment plant designs in Morocco, the systems are no longer used due to inconsistent gas quantities and poor gas quality (hydrogen sulfide). Based on this experience and low electricity prices, methane gas collection and reuse was not designed for facilities in Jordan. Nitrification A biofilm process was selected as the technology for nitrification because these systems are simple, reliable and cost less to operate than suspended growth systems. Two of the facilities presented use intermittent sand filters and two of the systems use recirculating sand filters for nitrification as well as additional solids and carbon removal. Upstream lagoons prevent excessive solids from prematurely clogging the filters. Operating procedures were developed to control the accumulation of biomass and to maintain an adequate level of oxygen in the sand filters for nitrification. The primary source of oxygen in the sand filters is diffusion of oxygen into the upper layers of the sand from the air. This effect is enhanced by frequent "tilling" of the sand on the surface. The tilling process involves turning the top 5 to 7 centimetres of sand to expose the bacteria growing on the sand grains to the surface air. The tilling process also breaks up the hard pan of solids and algae that tend to build up on the surface over time. Some oxygen will also enter the bottom of the sand filters through the open underdrains and their riser vent pipes. Flow-holding basins upstream of the sand filters hold and dose the flow intermittently, allowing the filters some time to rest and re-oxygenate. T Young, R Copithorn, J Karam, O Abu-Rayyan Beneficial products include irrigation water, reeds and dried biosolids for soil amendment RELIABLE LOW TECHNOLOGY FOR POLLUTION CONTROL IN SEMI-RURAL MOROCCO AND JORDAN Reed beds at Drarga.
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