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Title: Nitrogen transformation and wastewater treatment efficiency in algae-based and duckweed-based stabilization ponds
Authors: Zimmo, Omar
Al-Sa'ed, Rashed
Keywords: Sewage - Purification - Nitrogen removal;Sewage - Purification - Biological treatment;Organic wastes - Recycling;Sewage lagoons
Issue Date: 2-May-2005
Publisher: PALESTA
Source: Zimmo, O., and Al-Sa`ed, R. (2005). Nitrogen transformation and wastewater treatment efficiency in algae-based and duckweed-based stabilization ponds. In: Proc. Int. Conf. on Water: Values and Rights, May 2-4, 2005, Ramallah, Palestine
Abstract: A pilot plant experiment was carried out to determine the differences in nitrogen transformations in two systems for wastewater treatment: algae based stabilisation ponds (ABP) and duckweed (Lemna gibba) based stabilisation ponds (DBP). Each system consisted of a sequence of 4 equal ponds (3m length, 1m width and 0.9 m depth) in series and was fed with a constant flow rate of 0.4 m3/d of partially treated domestic wastewater from Birzeit University. Different nitrogen constituents have been monitored within each treatment system. The results show differences in the nitrogen transformations of the two systems during the 4 months monitoring period (May-August 1999), which started 5 months after the pilot plant start up and lasted for four months. The average total nitrogen (Kj-N+NO2--N+NO3--N) and ammonium (NH4+-N) in pond water were reduced more effectively in ABP (77% and 87% respectively) than in DBP (52% and 60%). Mass balances on total nitrogen indicated that this was because N-loss (probably due to denitrification and ammonia volatilisation) was higher in ABP (32 %) than in DBP (13%). Ammonia volatilisation might be the major part of nitrogen loss in ABP since pH values were greater than the pKa of ammonium (9.3). In, DBP, it’s not clear which mechanism (denitrification or ammonia volatilisation) is more important. N-loss in ABP was decreasing in the successive ponds within the system, probably due to reduction in the nitrogen concentration in the pond water. In DBP, N-losses were fairly constant (5-6.5%), except for pond number 1 where N-loss was only 1%. In DBP not nitrogen loss but nitrogen recovery via duckweed harvesting (34%) is the largest contribution to nitrogen removal. Average nitrate concentrations in the final effluent of ABP and DBP were 1.8 and 1.9 mg/L respectively. Higher DO concentrations in ABP (DO was over saturated most of the time) did not favor higher nitrification over DBP (DO range was 1 to 5 mg/L). In ABP, algae seemed to die-off and settle to the bottom of the ponds. This contributed to higher nitrogen accumulation (46% of the influent nitrogen) in comparison with DBP, where only 4% of the influent nitrogen was accumulated as detritus sediment, consisting of dead duckweed biomass. ABP as well as DBP are efficient treatment systems for control of nitrogen in domestic wastewater. Sediment accumulation and removal by volatilisation and/or denitrification in ABP and harvesting of duckweed in DBP are the major nitrogen removal mechanisms for nitrogen control in ABP and DBP, respectively.
Description: Proc. Intl. Conference on Water: Values and right, 2-4.05.2005 Palestine Academy for Science and Technology, Ramallah, Palestine
Appears in Collections:Institute of Environmental and Water Studies

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