Water Journal : Water Journal December 2011
technical features 80 DECEMBER 2011 water small wastewater systems One of the most difficult requirements of JS 895/2006 is the nitrate-nitrogen requirement. An initial feasibility study for the SCP identified that sand filters (either intermittent or recirculating), followed by reed beds, offered the most favourable low-maintenance technology capable of providing consistent oxidation of the high-strength ammonia-nitrogen concentrations present in the raw septage. However, in order for the sand filters to operate properly, unit operations were necessary upstream to reduce organic and solids loading rates. Sizing and unit process design of the treatment facilities was based primarily on operational data and operating experience obtained from Drarga, Morocco, with adaptations necessary to accommodate the more concentrated nature of septage and the differing environmental conditions. The primary differences between the two facilities are the capacity (Shobak is designed to handle up to 450m3/d, while North Shouneh is designed for 1,200m3/d), and the local climate conditions (Shobak is designed for a winter average temperature of 6.4°C, while North Shouneh is designed for a winter average temperature of 15.8°C). Shobak WWTP The Shobak WWTP is designed to receive an annual average of 350m3/d. The facility has been designed to accept an average of 425m3/d over eight summer months and 200m3/d over four winter months, with the ability to treat high flows of up to 450 m3/d for at least one summer month. Because of the cold winter temperatures encountered in the Shobak region, complete nitrification and denitrification using natural processes to continuously meet JS 895/2006 was deemed uneconomical under design conditions. Therefore, the Shobak WWTP was designed primarily for effluent evaporation. The Shobak WWTP for the treatment of septage uses natural, low-technology treatment provided by the following key process units: septage receiving and screening station; two settling/digestion reactors (each consisting of four 170m2 settling/digestion compartments); two 2,900m2 anaerobic settling lagoons; 10 300m2 intermittent sand filters; four 5,000m2 reed beds; and 30,000m2 of evaporation ponds (see Figure 3). The settling/digestion reactors and anaerobic lagoons were designed for a 5.0 day and 20 day HRT respectively. Five sand filters are dosed once per day at an average rate of 350mm. Although primarily designed for evaporation of the effluent, current treatment is capable of meeting reuse standards during parts of the year, particularly under lower loading rates than design. The facility has also been sited and designed to accommodate upgrade and expansion in the future should it be necessary. The facility started receiving septage in late January 2010 and one treatment train became filled and began completely processing wastewater at the beginning of July 2010. During the first 12 months of operation (February 2010 through January 2011) an average of 164 tankers delivered septage each month for an average influent quantity of 64m3/d. The highest septage quantities were received in June and July (maximum monthly average of 85m3/d). Plant performance data is presented in Table 5. Comparing the effluent quality results presented above against the Jordanian Irrigation Reuse Standards (JS893/2006) shown in Table 4, the average quality of effluents produced by the WWTP is in compliance with Class A. However, some of the samples taken (i.e., maximum values) exceeded Class A limits. All Table 5. Shobak WWTP performance (November 2010 through January 2011). Parameter Influent (mg/l) Settling/ Digestion (mg/l) Anaerobic Lagoon (mg/l) Sand Filters (mg/l) Reed Beds (mg/l) Removal Efficiency BOD 2,270.4 563.8 312.6 75.6 22.6 99.0% COD 4,515.4 1,070.4 704.0 172.0 70.2 98.4% TSS 2,048.0 492.4 354.0 129.0 20.0 99.0% TN 292.0 207.5 170.7 37.9 8.2 97.2% NO3-N 2.3 2.4 2.1 13.8 4.4 PO4 25.1 N/A N/A N/A 1.0 96.0% TDS 2,003 2,160 2,191 2,107 2,489 Fecal Coliform (MPN/100ml) 4.8 x108 N/A N/A N/A 25.6 Nematodes (eggs/5l) N/A N/A N/A N/A 0 Septic hauler unloading at Shobak.
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