Effect of nutrient concentration and pH on growth and nutrient removal efficiency of duckweed (Lemna minor) from natural solid waste leachate Jamshaid Iqbal Institute of Environmental Sciences and Engineering, National University of Sciences and Technology Islamabad, Pakistan jamshaidiqbal88@yahoo.com Dr. Muhammad Anwar Baig Institute of Environmental Sciences and Engineering, National University of Sciences and Technology Islamabad, Pakistan Abstract— This study aims to investigate the effect of nutrient concentration and pH of leachate on growth and nutrient removal efficiency of duckweed (Lemna minor). A batch experiment was conducted using pH range of 4-10 and two initial leachate dilutions with nutrient concentrations of N (90 and 20 mg L -1 ) and P (76 and 16 mg L -1 ) and effect of pH and initial nitrogen (N) and phosphorous (P) contents of natural leachate was investigated on growth and nutrient removal efficiency of Lemna minor. Nutrient removal rates of duckweed increase with an increase in initial nutrient concentration of leachate at all pH levels. At both leachate dilutions, pH range of 6-8 with an optimum of 7.1 is good for nutrient removal efficiency of duckweed from leachate. The highest rates of nitrogen (1.22 g m -2 day -1 ) and phosphorous (0.95 g m-2 day-1) removal were achieved from more concentrated leachate at pH 7.1. Growth rate of duckweed decreases with an increase in initial nutrient concentration of leachate at all pH levels. Maximum growth rate of duckweed (19.6 g m2 day-1) was achieved at pH 7.1 from less concentrated leachate. Nitrogen and phosphorous uptake in duckweed biomass was higher in less concentrated leachate at all pH values. Optimum pH for N and P uptake by Lemna minor is 7.1 at both leachate dilutions. At this pH duckweed showed 94 % and 91 % uptake of N and P respectively from less concentrated leachate. Key Words— leachate, duckweed, lemna minor, nutrients, pH, removal rate, growth rate. I. INTRODUCTION Leachate is the high strength wastewater. At open waste dumping sites it is produced by percolation of rainwater through solid waste layers [1]. Various physic-chemical and bio-chemical processes in solid waste transfer variety of pollutants from waste streams into percolating rain water [2]. A typical leachate contains high amounts of recalcitrant substances, such as humic and fulvic acids, xenobiotics and pesticides, heavy metals and inorganic macro constituents (Ca, Mg, K, Na, NH4, Cl, HCO3 and SO4 etc.) [3,4]. Unattended leachate poses serious environmental problems such as contamination of surface and ground water, soil contamination and direct and indirect hazards for human health, flora and fauna and ecosystems [5,6]. Nutrients content of leachate may be as high as 13,000 mgL -1 of organic nitrogen [6], up to 400-3000 mgL -1 of ammonia-nitrogen and 3000 mg L -1 of phosphate [7, 8]. In Pakistan, concentrations of nitrogen and phosphorous in leachate is usually higher than national environmental standards [9]. By systematic planning and conditions optimization, the high nutrient content of leachate makes it the favored media for growth of aquatic plants. Aquatic plants convert nutrients in growth media into valuable plant biomass making full use of the postharvest biomass as animal feed, fertilizer and for production of protein rich byproducts [10]. Duckweed is amongst the promising aquatic plants having ability to absorb large amounts of nutrients from eutrophicated wastewater and has high growth rates [11,12,13]. Duckweed is a small floating macrophyte belonging to family Lemnaceae of monocotyledon plants. Duckweed has 37 species belonging to 4 genera (Lemna, Spirodela, Wolffia and Wolffiella) [14]. It is reported that duckweed based swine lagoon treatment system can remove up to 83.7% and 89.4% of total nitrogen (TN) and total phosphorus (TP) respectively from the media [15]. High level of nutrients tolerance in duckweed is of particular importance for treatment of high strength leachate. Lemna minor specie of duckweed has enormous potential of nutrients removal from wastewaters of high strengths [16]. Cheng et al [17] has reported a growth rate of L. minor close to 29 g m-2 day-1 and Total Kjeldahl Nitrogen (TKN) and Total Phosphorous (TP) uptake of 90 % and 88.6 % respectively from high strength swine lagoon. pH is one of the important environmental factors affecting the uptake of chemicals and their distribution in living plants [18]. The pH of the growth medium determines the ratio between the NH4 + (preferred form of nitrogen for duckweed) and un-dissociated NH3 [19]. Some researchers have investigated the effect of pH on duckweed growth using artificial growth media under artificial conditions of light intensity, temperature and humidity [20]. However, the use of natural leachate for duckweed growth under the natural climatic conditions is least explored area so far This study investigates the effect of pH and initial concentrations of nitrogen and phosphorous on nutrient removal and growth of duckweed (Lemna minor) grown on natural leachate under the natural climatic conditions of Islamabad, Pakistan. Study provides an input to design the