The aim of the study presented was to implement a process model to simulate the dynamic behavior of lad-scale process for TPAD (temperature phased anaerobic digestion) process of composite substrate mixed dog food with flour. The model concept implemented in the simulation software MATLAB 6.1 is a derivative of the IWA Anaerobic Digestion Model No.1 (ADM1) that has been developed by the IWA task group for mathematical modeling of anaerobic process. In the present study the original model concept has been adapted and applied to replicate TPAD process.
In this experimental work, HRT is controlled 4.2 d and 11.5 d of each reactor. By contrast, SRT is decreased stepwise from 230d to 23d. The organic loading rate is 15.4 g COD/d, 25.2 g COD/d and 35.7 g COD/d. The COD removal efficiency is consistently about 46.3%, 50.0% and 51.3% at the thermophilic reactor, and that is about 95.3%, 95.9% and 96.2% throughout the whole process completely. The methane conversion rate is 56.3%, 60.9%, and 64.4% in each organic loading rate. In additions, the values of yield in the whole system are 0.59, 0.61 and $0.64 g CH_4 /g COD_{removed}$ with each organic loading rate.
In the model work, ultimately, 17 parameters were identified based on the sensitivity analysis. Among them, methane, VFAs, ammonia, and soluble COD are estimated to these parameters. Soluble COD has the most sensitive to these parameters. Of all parameters sensitive to TPAD process, there are maximum specific uptake rate $(k_{m.pro}, k_{m.ac}, k_{m.c4})$, disintegration constant $(k_{dis 35/55})$, and decay rate $(k_{dec})$. In the model output of methane production, at the beginning step, model output is not accord with experimental data, because model is not sensitive to varying points. That is, it means that ADM1 have to modify of the problems of these parts.
In the batch test, ADM1 can be estimated throughout using the simulation with variable of Total ammonia nitrogen (TAN) concentration and pH. Model simulations offered good information except intermediate course, where microorganism had adapted to a new culture. However, microorganism kinetics and behaviors on acclimation problem can not be described as mathematical model completely. Throughout this study, inhibitor should influence on not only the monod maximum specific substrate utilization rate but also the yield, that is, ADM1 can not describe these parts without any modification.
Finally, due to the high number of parameters in the structured model, it was necessary to develop a customized procedure that limited the range of parameters to be estimated. The accuracy of the optimized parameter sets has been assessed against experimental data. Under these conditions, the model predicted reasonably well the dynamic behavior of TPAD process.
본 연구의 목적은 밀가루와 개 사료를 동일하게 혼합하여 만든 복합 기질을 이용하여 lab-scale 단위로 TPAD (temperature phased anaerobic digestion) 공정을 운전하는 것이다. 획득된 실험 결과를 이용하여 수학적 모델링을 위한 IWA Task group에 의해 제시한 ADM1 (anaerobic digestion model No.1) 을 적용해 보고 평가하는 것이다.
연속 공정에서 각 반응조의 HRT는 4.2일과 11.5일로 운전하였다. 반면에 SRT는 ASBR 형태인 중온조의 경우 230일에서 단계적으로 23일까지 운전하였으며 step feed 방식인 고온조는 4.2일로 운전하였다. OLR (organic loading rate)는 15.4 g COD/d, 25.2 g COD/d, 그리고 35.7 g COD/d로 운전하였으며, 고온조의 COD 제거 효율은 각 OLR에 따라 46.3%, 50.0%, 51.3%이었다. 전체 공정에서의 COD 제거 효율은 95.3 %, 95.9%, 96.2%의 높은 유기물 제거 효율을 보였다. 또한 전체 공정에서 메탄 전환율은 56.3%, 60.9%, 64.4%였으며 각각 OLR에 따른 수율(yield)은 0.59, 0.61, $0.64 g CH_4/g COD_{removed}$ 로 분석되어졌다.
모델에선, 메탄, VFAs, 암모니아, 그리고 SCOD의 대상 물질에 대해 17개 변수의 민감도를 분석 하였다. 그 중 SCOD의 대상 물질에 대해 민감한 변수들이 가장 많았으며, TPAD 전체 공정에 대해 민감한 변수들로는 maximum specific uptake rate $(k_{m.pro}, k_{m.ac}, k_{m.c4})$, disintegration rate $(k_{dis 35/55})$, and decay rate $(k_{dec})$ 이었다. 변수 추정후의 모델값은 실험값에 거의 일치하였으며, 모델의 검증 단계 (model verification)에서 OLR이 변화는 변곡점에서는 두개 값 사이에 차이가 있음을 알수 있었다. 그 이유는 생화학 반응에서 추진력 (driving force)으로 설명할 수 있는데, 모델에서의 변이는 미생물의 농도와 관계가 있지만 실제 실험에서는 기질의 농도가 변이값을 좌우하는 인자이기 때문이다.
