| With high moisture content and rich in easily degradable organic matters, food waste(FW) is easily perishable while at the same time there is a huge potential of resources and energy by recycling it. Therefore, it is popular to separate FW from the municipal solid wastes and collect it separately for reuse. Compared with a lot of other techniques of treating FW, anaerobic digestion(AD) has its unique advantages so that it becomes the preferred technology. However, the characteristic of high easily degradable organic matters, oil, protein and salt content, combined with anaerobic microorganisms in the system which are very sensitive to process disturbance, the AD of FW usually has problems of instability. Organic loading rate(OLR) is regarded as the important parameter which influences the stability of AD process. In consequence, full-scale digesters usually run at low OLR, taking a loss in capacity utilization and profitability into account to prevent process failures. So far, there are great differences of the maximum OLR in many studies about AD of FW system. Its main reason is that the traditional OLR only relates to the substrate and the reactor volume, does not involve the microbes which is the core of the AD system. For different AD systems, the amount of microbes may directly lead to different final OLR. Therefore, this research mainly carried out from three aspects. Firstly, this study was to verify the reactor performance and process stability associated with biomass concentrations. Secondly, this paper discussed whether the new index of sludge loading rate(SLR) had better effect on the stability of process characterization. Thirdly, this study was to reveal the effect of SLR on the reactor performance and the process stability. In order to provide new ideas for the selection of operation parameters of AD. The results by batch and continuous test were as follows.(1)During the batch and semi-continuous tests, reactor performance and process stability were both closely related to the sludge concentration, and the changes of the parameters were more consistent with the change of SLR, SLR as a characterization index was better than OLR.(2)Throughout the batch experiment, the S/I ratio ranged from 0.33gVS·g-1VSS to 6gVS·g-1VSS. When the S/I ratio was less than 2gVS·g-1VSS, each experimental group did not appear any acidification inhibition. With S/I ratio increased to 2 and 3 gVS·g-1VSS, there were acidification inhibition of varying degrees. The reactor performance and process stability related to the specific OLR and sludge concentration. Thus, when S/I ratio was in the critical value and the system was in transition period of acidification, its representation of the performance and stability was not consistent. When S/I ratio further increased to more than 3 gVS·g-1VSS, the system was severely inhibited, specific methane yield significantly decreased, SMA significantly increased, and the S/I ratio at this time was in the range of overload.(3)During the whole semi-continuous test, SLR had little change from 0.0906 gVS·g-1VSS·d-1 to 0. 129 gVS·g-1VSS·d-1. At the first stage, the SLR gradually increased from 0.0906 gVS·g-1VSS·d-1 to 0.1128 gVS·g-1VSS·d-1 caused by the sludge washout, so that each parameter displayed system on the verge of instability. At the second and third stage, SLR maintained at 0.097 ± 0.001 and 0.126 ± 0.002 gVS·g-1VSS·d-1, respectively, the systems were stable and efficient. However, because of ammonia nitrogen accumulation of the third stage inhibiting the activity of methane bacteria, the system ultimately collapsed in low OLR and SLR. |
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