Fax +44 (0)2380 677519 2 AbstractPurpose: A trace element supplementation strategy previously shown to be effective in mesophilic conditions was tested for thermophilic digestion of source segregated domestic food waste.Method: Inoculum from a mesophilic anaerobic digester treating municipal wastewater biosolids was successfully acclimated to thermophilic temperature (55 o C) with food waste as a substrate. Four laboratory-scale digesters were maintained at a loading of 2 g VS l -1 day -1 with one pair receiving trace elements (TE) supplementation. Two more pairs of digesters were incrementally loaded to 3 and 4 g VS l -1 day -1 , respectively, and also received TE.Results: All digesters performed well for the first 3-4 months of operation, but volatile fatty acid (VFA) concentrations in those without TE showed no recovery from an initial small accumulation. On continued operation, VFA concentrations increased in all digesters, especially those at higher loading rates or without TE supplementation, reaching >30 g l -1 .Under these meta-stable conditions, a deliberate disturbance to daily feeding (cessation then resumption) led to acetic acid accumulation, a fall in pH and a sharp increase in the ratio of partial to intermediate alkalinity. Increases in VFA corresponded to an increasing total ammonia nitrogen concentration which appeared to become inhibitory at ~2500 mg N l -1 . It has been shown that in mesophilic conditions accumulation of VFA can be prevented by supplementing with selected trace elements [17][18][19][20]. Mesophilic food waste digesters supplemented with trace elements have been shown to operate with good gas production and low VFA concentrations at ammonia concentrations in excess of 6000 mg l -1 , but with a purely hydrogenotrophic methanogenic population; and a mechanism by which trace element addition can prevent VFA accumulation at high ammonia concentrations has been put forward [18]. Selenium, which is present only in low concentrations in food waste, has been shown to be essential in preventing propionic acid accumulation by providing the co-enzymes 4 necessary for the reduction of formate, one of the metabolic products of propionate degradation. At higher organic loading rates (OLR) additional cobalt is also required. This is thought to be necessary as in these high ammonia conditions all of the organic carbon is converted to carbon dioxide through syntrophic acetate oxidation by the reverse WoodsLjungdahl pathway; in conjunction with the reduction of carbon dioxide to methane by the hydrogenotrophic route, this leads to an increase in co-enzyme demand. Where formate oxidation does not occur there is an accumulation of propionic acid and other longer-chain VFAs, leading eventually to a fall in pH and cessation of methanogenesis [18]. ConclusionsThe current study investigated the extent to which a trace element addition strategy successfully applied in mesophilic conditions could prevent VFA accumulation in thermophilic digesters operating on source segregated food waste, in conditions...

Ammonia toxicity was investigated in mesophilic (37 o C) and thermophilic (55 o C) digesters using high and low-nitrogen food wastes (FW). Mesophilic inoculum was successfully acclimated to thermophilic conditions by a step change in temperature followed by incremental increases in organic loading rate (OLR). Digestion performance and stability were monitored via volatile fatty acid (VFA) profiles, alkalinity, specific methane production (SMP) and volatile solids (VS) destruction. High-nitrogen mesophilic digesters stabilised by day 70 and responded well to increases in OLR, with a SMP of 0.45 L CH 4 g -1 VS, stable pH, and VFA <0.2 g L -1 . Thermophilic digesters fed on high and low-nitrogen FWs showed almost identical responses to acclimatisation. Behaviour then deviated, with high-nitrogen digesters accumulating VFA. Stable pH could be maintained for up to 310 days before eventual failure at total ammonia nitrogen (TAN) concentration >5.0 g N L -1 , although accumulation of propionic and other longer-chain VFA began at TAN ~3.5 g N L -1 . The low-nitrogen digesters showed no VFA accumulation, and had a SMP of ~0.39 L CH 4 g VS L -1 day -1 with 91% VS destruction. After 384 days the TAN concentration was increased from ~0.7 g N L -1 by urea addition. This resulted in progressive VFA accumulation in one digester when TAN reached ~3.5 g N L -1 , while stable operation at very low VFA was possible at up to ~2.5 g N L -1 in the second digester. The results confirmed acclimatisation to thermophilic conditions was possible on a far shorter timescale than to high TAN concentrations.

Wastewater from seafood industry contains high concentrations of organic matter, nitrogen compounds, and solid matter. Constructed wetland can be used as tertiary treatment and for nutrient recycling. This research studied the performance of nitrogen and suspended solids removal efficiency of a constructed wetland treating wastewater from a seafood-processing factory located at Songkhla, southern Thailand. The existing constructed wetland has dimensions of 85 m, 352 m and 1.5 m in width, length and depth respectively, with an area of about 29,920 m2. The water depth of 0.30 m is maintained in operation with plantation of cattails (Typha augustifolia). Flow rate of influent ranged between 500-4,660 m3/d. Average hydraulic retention time in the constructed wetland was about 4.8 days. Influent and effluent from the constructed wetland were collected once a week and analyzed for pH, temperature, dissolved oxygen (DO), biochemical oxygen demand (BOD5), Suspended solid (SS), total Kjeldahl nitrogen (TKN), ammonia nitrogen (NH3-N), organic nitrogen (Org-N), nitrate (NO3-N), and nitrite (NO2-N). The average removal efficiencies of BOD5, SS, TKN, NH3-N, and Org-N were 84%, 94%, 49%, 52% and 82%, respectively. It was found that the constructed wetland acting as a tertiary treatment process provided additional removal of BOD5, SS and TKN from wastewater from the seafood industry.

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