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The performance of a laboratory-scale anaerobic acidogenic fermenter fed with a mixture of blended kitchen food-waste and primary sludge from a sewage treatment plant was investigated for the production of volatile fatty acids (VFA). The operating variables for acidogenic fermentation were kitchen food-waste content (10 and 25 wt %), hydraulic retention time (HRT: 1, 3 and 5 days), temperature (ambient: 18 ± 2• C, and mesophilic: 35 ± 2 • C) and pH (varied from 5.2 to 6.7). The experimental results indicated that effluent VFA concentrations and VFA production rates were higher at ambient temperature than at mesophilic conditions. The net amount of VFA with 10 wt % food-waste increased up to 920 mg dm −3 with an increase of HRT, but contrasting results (a decrease of 2610 mg dm −3 ) were found due to the conversion of VFA into biogas in the case of 25 wt % food-waste, which increased significantly at HRT of 3-5 days. In terms of biogas composition (CO 2 and CH 4 ), the organic matter was converted into CO 2 through the oxidative pathway by facultative species at low temperature while mesophilic temperature and optimum pH (6.3-7.8) played a pivotal role in increasing rate of conversion of VFA into biogas by methanogenesis. Rates of VFA production and their conversion are dependent on the food-waste content in the mixture. Yet, the higher concentration of food-waste (25% compared with 10%) did not produce VFA proportionally due to the increased rate of conversion of VFA into gaseous products. The maximum VFA production rate (0.318 g VFA produced g −1 VS fed day −1 ) was achieved in the 10 wt % food-waste at ambient temperature and at a 5-day HRT.

Nitrogen removal in piggery waste was investigated with the combined SHARON-ANAMMOX process. The piggery waste was characterized as strong nitrogenous wastewater with very low C/N ratio. For the preceding SHARON reactor, ammonium nitrogen loading and conversion rates were 0.97 kg NH4-N/m3 reactor/day and 0.73 kg NH4-N/m3 reactor/day, respectively. Alkalinity consumption for ammonium conversion was 8.5 gr bicarbonate utilized per gram ammonium nitrogen converted to NO2-N or NO3-N at steady-states operation. The successive ANAMMOX reactor was fed with the effluent from SHARON reactor. Nitrogen loading and conversion rates were 1.36 kg soluble N/m3 reactor/day and 0.72 kg soluble N/m3 reactor/day, respectively. The average NO2-N/NH4-N removal ratio by ANAMMOX reaction was 2.13. It has been observed that Candidatus "Kuenenia stuttgartiensis" were dominated in the ANAMMOX reactor based on FISH analysis.

The nitrogen-removal performances of three full-scale piggery wastewater treatment plants, with different organic and nitrogen loads, at the capacity ranges of 95 to 130 m 3 /d, were compared in this study. Plants 1 and 2 can be characterized as the modification of anoxic-aerobic operating systems, while an anaerobic and anoxic-aerobic system was used in plant 3. The influent piggery wastewater concentration for plant 1 was relatively lower, but with higher organic and nitrogen loads, resulting in higher chemical oxygen demand (COD) and ammonium-nitrogen in effluent. Plant 2 was operated with strong piggery wastewater, resulting in a higher operating temperature. The high temperature could inhibit the nitrifying activity in plant 2. Although plant 3 was operated with a higher influent total COD-to-total Kjeldahl nitrogen ratio (TCOD:TKN), an additional external carbon source was required to polish the final effluent to remove nitrogen. Influent COD in plant 3 was used in the anaerobic-anoxic reactor for both methane (CH 4 ) production and denitrification. Based on various mass balances, including caloric, COD, and alkalinity, the key elements for the successful nitrogen removal from the piggery waste were reactor temperature (less than 358C), influent TCOD:TKN (greater than 6), and alkalinity-to-TKN ratio (greater than 3). Water Environ. Res., 77, 381 (2005).