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Pre-acidification of a Synthetic Dairy Wastewater in Continuously Stirred Tank Reactors

Xiong, Can LU (2019) VVAM01 20191
Chemical Engineering (M.Sc.Eng.)
Abstract
Two-stage anaerobic digestion is considered as a sustainable and efficient way to deal with dairy effluent, and is commonly applied. The pre-acidification happening during the first stage of this process could be used to buffer the complex conditions in the initial dairy effluent, as well as produce intermediary product such as volatile fatty acids (VFA), and it is essential to be controlled. Various types of reactors have been used studying this process, among which, continuously stirred tank reactor (CSTR) is common with its special benefits. During the pre-acidification process, the adjustment of hydraulic retention time (HRT) and pH is crucial to affect the performance of reactors. In order to compare the performance under different... (More)
Two-stage anaerobic digestion is considered as a sustainable and efficient way to deal with dairy effluent, and is commonly applied. The pre-acidification happening during the first stage of this process could be used to buffer the complex conditions in the initial dairy effluent, as well as produce intermediary product such as volatile fatty acids (VFA), and it is essential to be controlled. Various types of reactors have been used studying this process, among which, continuously stirred tank reactor (CSTR) is common with its special benefits. During the pre-acidification process, the adjustment of hydraulic retention time (HRT) and pH is crucial to affect the performance of reactors. In order to compare the performance under different operation conditions, CSTRs were used to treat a synthetic dairy effluent in this work. This experiment was divided into two periods. One is under the pH of 4.9, another is under the pH of 4.0. The first condition was operated for 55 days. Then the pH in both reactors was adjusted at 4.0 for another 22 days. The volatile fatty acids (VFA) as the major fermentation product was analyzed. The results shows that at the pH of 4.9, the acidification degree in the CSTR with the HRT of 18h reached 80%, while the one with lower HRT could only reach 18%. Besides, results also indicate that HRT also has impact on the distribution of acids. As for the influence of pH, the results show that after the pH was adjusted down to 4.0, the total amount of VFA production decreased significantly especially for the one with the HRT of 18h (the acidification degree dropped down from 80% to 15%). Moreover, the decreased pH had a distinct impact on the VFA distribution. Before reducing the pH butyric acid was the most generated acid, followed by propionic acid and acetic acid. After the pH dropped, the mostly produced VFA was acetic acid, and at the same time, the proportion of butyric acid dropped significantly. The fermentation product consists not only of VFA which was mainly analyzed in this work, but also of other compounds such as formic acid and lactic acid. However, other fermentation compounds were not specifically analyzed in this work. (Less)
Popular Abstract
Pre-acidification performances of a dairy wastewater under different hydraulic retention times and pH.
Pre-acidification is the initial process during anaerobic digestion treatment. This study evaluated different performances of pre-acidification with reduced hydraulic retention time (HRT) and pH value. Since these two factors not only affect the efficiency of pre-acidification, but also greatly related to financial issues during treatment processes.
The demand of dairy product grows rapidly, and dairy industries are accompanied by large amounts of dairy effluent. What are both efficient and cost-effective ways to treat dairy effluent? Anaerobic digestion (AD) as one of the biological methods is attractive because it could reduce sludge... (More)
Pre-acidification performances of a dairy wastewater under different hydraulic retention times and pH.
Pre-acidification is the initial process during anaerobic digestion treatment. This study evaluated different performances of pre-acidification with reduced hydraulic retention time (HRT) and pH value. Since these two factors not only affect the efficiency of pre-acidification, but also greatly related to financial issues during treatment processes.
The demand of dairy product grows rapidly, and dairy industries are accompanied by large amounts of dairy effluent. What are both efficient and cost-effective ways to treat dairy effluent? Anaerobic digestion (AD) as one of the biological methods is attractive because it could reduce sludge production, and produce utilized biogas. Pre-acidification is the initial process in AD with its main product of volatile fatty acids (VFA), this product is used to produce utilized biogas in further steps. What could be done during pre-acidification in order to save space and money? It is noteworthy that generally low HRT associates with financial benefits and low pH could reduce the cost for buffer solutions during pre-acidification, but it might also affect the performance of this process.
What would happen during pre-acidification if the HRT is decreased by 67% from the conventional HRT (18h), or if the pH value is decreased to 4.0, while the conventional pH is around 5? This project is part of a project carried out at company AnoxKaldnes, Veolia, Lund, focusing on the analysis of pre-acidification of a synthetic dairy effluent at reduced HRT (6h) and pH (4.0), in two parallel continuously stirred tank reactors (CSTR), in comparison with the longer HRT (18h) and higher pH (4.9) and it. Volatile fatty acids as the major product from pre-acidification were the most interesting parameters to observe and analyze.
According to the results, both HRT and pH are crucial factors impacting the pre-acidification process, with regard to VFA production. In this case, the longer HRT resulted in larger amounts of VFA generated. The CSTR performed at an acidification degree up to 80% with the HRT of 18 h, it is reasonable to state that 18 h is suitable for the pre-acidification process, with this specific dairy wastewater, while 6h is too short for the reactor to perform well. Studies on more varying HRTs between 6 h and 18 h could be more interesting in future work.
Besides, the results indicates that pH buffering is important during pre-acidification. A low pH at 4.0 remarkably inhibited the generation of VFA, compared with the pH of 4.9. As for the acids distribution, at a higher pH value, butyric acid and propionic acid were mostly generated in the reactors, while at the pH of 4.0, the acetic acid became the main component in the produced VFA. It indicates that it is possible to make adjustments on HRT and/or pH in order to get specific types of acids during the pre-acidification process. (Less)
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author
Xiong, Can LU
supervisor
organization
alternative title
Pre-acidification performances of a dairy wastewater under different hydraulic retention times and pH
course
VVAM01 20191
year
type
H2 - Master's Degree (Two Years)
subject
keywords
pre-acidification process, hydraulic retention time, soluble chemical oxygen demand transformation into fermentation product, volatile fatty acids, distribution, water engineering, environmental engineering, vattenförsörjningsteknik, avloppsteknik
report number
2019-05
language
English
id
8982391
date added to LUP
2019-07-04 13:50:22
date last changed
2019-07-04 13:50:22
@misc{8982391,
  abstract     = {Two-stage anaerobic digestion is considered as a sustainable and efficient way to deal with dairy effluent, and is commonly applied. The pre-acidification happening during the first stage of this process could be used to buffer the complex conditions in the initial dairy effluent, as well as produce intermediary product such as volatile fatty acids (VFA), and it is essential to be controlled. Various types of reactors have been used studying this process, among which, continuously stirred tank reactor (CSTR) is common with its special benefits. During the pre-acidification process, the adjustment of hydraulic retention time (HRT) and pH is crucial to affect the performance of reactors. In order to compare the performance under different operation conditions, CSTRs were used to treat a synthetic dairy effluent in this work. This experiment was divided into two periods. One is under the pH of 4.9, another is under the pH of 4.0. The first condition was operated for 55 days. Then the pH in both reactors was adjusted at 4.0 for another 22 days. The volatile fatty acids (VFA) as the major fermentation product was analyzed. The results shows that at the pH of 4.9, the acidification degree in the CSTR with the HRT of 18h reached 80%, while the one with lower HRT could only reach 18%. Besides, results also indicate that HRT also has impact on the distribution of acids. As for the influence of pH, the results show that after the pH was adjusted down to 4.0, the total amount of VFA production decreased significantly especially for the one with the HRT of 18h (the acidification degree dropped down from 80% to 15%). Moreover, the decreased pH had a distinct impact on the VFA distribution. Before reducing the pH butyric acid was the most generated acid, followed by propionic acid and acetic acid. After the pH dropped, the mostly produced VFA was acetic acid, and at the same time, the proportion of butyric acid dropped significantly. The fermentation product consists not only of VFA which was mainly analyzed in this work, but also of other compounds such as formic acid and lactic acid. However, other fermentation compounds were not specifically analyzed in this work.},
  author       = {Xiong, Can},
  keyword      = {pre-acidification process,hydraulic retention time,soluble chemical oxygen demand transformation into fermentation product,volatile fatty acids,distribution,water engineering,environmental engineering,vattenförsörjningsteknik,avloppsteknik},
  language     = {eng},
  note         = {Student Paper},
  title        = {Pre-acidification of a Synthetic Dairy Wastewater in Continuously Stirred Tank Reactors},
  year         = {2019},
}