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هدف از این مطالعه تصفیه فاضلاب غلیظ چغندر قند به وسیله پایلوت های بی هوازی بسترثابت با جریان بالارو (UAFB) می باشد. سه بیوراکتور بسترثابت (60 لیتری) با آکنه های استاندارد و صنعتی پرشده و سپس با باکتری های بی هوازی (ناشی از کود مرغی، کود گاوی، لجن بی هوازی تصفیه خانه فاضلاب شهری) لقاح گذاری گردیدند و پس از راه اندازی در دمای 32–34 °C با زمان ماند هیدرولیکی 20 ساعت و اکسیژن مورد نیاز شیمیایی (COD) بین 2000–8000 mg/L بهره برداری گردیدند. تحت این شرایط ماکزیمم راندمان 93 - 75 درصد در کاهش ترکیبات آلی در راکتور مشاهده گردیدند. راکتور پرشده از آکنه های استاندارد (pall rings) از جنس پلی پروپیلن (PF) با سطح موثر 206 m2/m3 دارای عملکرد بهتری نسبت به راکتور پر شده از آکنه های صنعتی (rashing ring) با جنس پلی اتیلن (PE) و سطح مخصوص 134 m2/m3 و راکتور پرشده با آکنه های پلی وینیل کلراید (PVC) 50 m2/m3 داشتند. نتایج نشان داد که 3 الی 7 درصد کاهش در راندمان PE و 10–16% کاهش در راندمان PVC در مقایسه با آکنه های استاندارد وجود دارد. این تحقیق اساس خوبی برای مقایسه اثر اکنه در کاهش راندمان یک سیستم محسوب می گردد.
لغات کلیدی: بیوپروسس های بی هوازی (UAFB) ، فاضلاب چغندر قند، اکنه های فیلتر بی هوازی، تصفیه فاضلاب صنعتی
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Bioresource Technology 98 (2007) 3080–3083
Treatment of beet sugar wastewater by UAFB bioprocess
Mehrdad Farhadian (Isfahan High Education and Research Institute, PWIT, Iran)
Mehdi Borghei (Sharif University of Technology-BBRC, Tehran, Iran)
Valentina V. Umrania (M.V.M. Sc. and HSc. College, Saurashtra University, Rajkot, India)
Received 13 July 2006; received in revised form 20 October 2006; accepted 22 October 2006
Available online 27 March 2007
The aim of this work was to study the treatment of strong beet sugar wastewater by an upflow anaerobic Fixed bed (UAFB) at pilot plant scale. Three Fixed bed bioreactors (each 60 L) were Filled with standard industrial packing, inoculated with anaerobic culture (chicken manure, cow manure, anaerobic sludge digested from domestic wastewater) and operated at 32–34 °C with 20 h hydraulic retention time (HRT) and influent COD ranging between 2000–8000 mg/L. Under these conditions the maximum efficiency of organic content reduction in the reactor ranged from 75% to 93%. The reactor Filled with standard pall rings made of polypropylene with an effective surface area of 206 m2/m3 performed best in comparison to the reactor Filled with cut polyethylene pipe 134 m2/m3 and reactor Filled with PVC packing (50 m2/m3). There was 2–7% decrease in efficiency with PE while it was 10–16% in case of PVC when compared to standard pall rings. The study provided a very good basis for comparing the effect of packing in reduction efficiency of the system.
© 2007 Elsevier Ltd. All rights reserved.
Keywords: Anaerobic bioprocesses; UAFB; Beet sugar wastewater; Anaerobic Filter packing; Industrial wastewater treatment
Anaerobic treatment of concentrated wastewater is widely accepted practice in the industry. It has several advantages over aerobic processes, which include the use of less energy due to omission of aeration, the conversion of organic matter to methane which is an energy source by itself and can be used to supply some of the energy requirement of the process. Lower production of sludge, which reduces sludge disposal costs greatly and low level of maintenance, are other benefits of anaerobic processes (Cakira and Stenstromb, 2005; Shin et al., 2005). Anaerobic systems are more suitable for handling high pollution load wastewaters, even with shorter hydraulic retention times and high organic loading rates where high substrate removal efficiencies can be expected. Further it tolerates higher hydraulic and organic over loading compared to other conventional systems. Due to its operation at lower HRT, it requires smaller volumes. It is less expensive to construct, to operate and to maintain.
During anaerobic bioprocesses organic pollutants are degraded by consortia of many microbial strains through multiple degradation steps such as hydrolysis/fermentation, acetogenesis and methanogenesis. These anaerobic microbes, including fermentative bacteria, acetogenic bacteria and methanogens usually form a syntrophic relation (Liu et al., 2002). Anaerobic treatment enables industry to comply with the stricter pollution control regulations, and also to satisfy the search for greater efficiency, better economy and the use of natural energy sources (Kusum Lata et al., 2002).
High rate anaerobic biological reactors may be classified into three broad groups depending on the mechanism used to achieve biomass detention, namely Fixed-film, suspended growth, and hybrid systems. There are currently more than 900 full-scale installations in the world today, such as up flow anaerobic sludge blanket (UASB) (Parawira et al., 2005), anaerobic Filter (AF) anaerobic attached film expanded bed’ (AAFEB) reactor (Connaughton et al., 2006), anaerobic baffled reactor, and anaerobic sequencing batch biofilm reactor (AnSBR) (Venkata Mohan et al., 2005). The upflow anaerobic Filter is one of the earlier designs and its characteristics are well defined. It is also a process which is based on relatively simple technology (Saravanan and Sreekrishnan, 2006). In engineering terms, it is not as complex as fluidised bed reactor and in biological terms it does not require the formation of a granular sludge, a prerequisite for the up flow sludge blanket reactor usually very difficult to maintain. Also, Fixed-film processes are inherently stable and resistant to organic and hydraulic shock loading (Qureshi et al., 2005).
Generally, anaerobic bioreactors are ideal for the treatment of food industry wastewaters. Sugar industry effluents which are high in organic concentration are good examples. There has been much interest in the application of anaerobic process for treatment of beet sugar waste water industries, mainly by UASB process. Some research has been carried out on anaerobic biofilteration mainly on selection of a suitable packing media. Different materials have been tested as support media for biomass retention in anaerobic biofilter. The performance of these materials appears to be directly related to the ease with which bacteria can become entrapped or attached. It has been stated that the surface state is important (Bouallagui et al., 2005).
The aim of this work was to study the effect of important factors for start up and operation of anaerobic biofilters. The effect of surface area on degree of organic removal in terms of COD removal under upflow conditions using beet sugar waste water was investigated.
2.1. Construction of bioreactors
Three Fixed bed bioreactors similar in shape and volume (60 L) were constructed and were used in this study. Each reactor was Filled with different packing in shape and in material with specifications shown in Table 1. The reactor B1 was Filled with pall rings made of polypropylene. Reactor B2 contained polyethylene rashing ring type packing. Reactor B3 was Filled with polyvinyl chloride (PVC) rashing rings as packing media. The temperature of reactors under steady state conditions were maintained in the range 32– 34 °C with industrial heater jackets. Peristaltic pumps were used for feeding the reactors at controlled flow rate.
Physical characteristics of bioreactors
Bioreactor Material Diameter Effective Packing Surface
of of column volume material area
column (cm) (L) and kind (m2/m3)
Bioreactor 1 PVC 15 60 PP–Pall rings 206
Bioreactor 2 PVC 15 60 PE–Rashing 50
Bioreactor 3 PVC 15 60 PVC–Rashing 134
The initial inoculation of the reactors was done with a mixture of anaerobic digested activated sludge taken from a domestic wastewater treatment plant sludge digester, chicken manure and cow manure. It was mixed thoroughly and incubated with molasses of beet sugar for one month at temperature 37 °C and pH was adjusted in the range from 7.00 to 7.5 for the adaptation of microbial growth. After that time period it contained TKN 2240 mg/L, TP 190 mg/L and alkalinity 6432 mg CaCO3/L. Also, the final concentration of sludge was 15,415 mg/L, TSS 2.54% and VSS 57.8%. Then each bioreactor was Filled with 67% of inoculum prepared at start-up stage.
2.3. Feeding of bioreactors
A solution of diluted beet sugar molasses with added nutrients was used as feed for bioreactors.
By using different concentration of molasses reactor feed with COD’s in the order of 5000–10,000 mg/L could be prepared. Urea and ammonium phosphate were used as nitrogen and phosphorous supplements. Average composition of 1 g beet sugar molasses in 1 L water was: TKN 10.25, Fe2+ 0.20, Ni2+ 0.08, Zn2+ 0.25, Mn2+ 0.04 and S2. 4.04 mg/ L, COD and BOD5 were 710 and 488 mg/L, respectively.
2.4. Analytical procedures
Influent and effluent samples were analyzed for COD, BOD5, TSS, SS, TKN, Alkalinity, pH in accordance with standard method laboratory procedure (Clesceri et al., 1998).
3. Results and discussion
During a period at three months, start-up for every bioreactor indicated that various parameters such as temperature, pH, alkalinity, OLR, HRT, VFA, and recycle ratio, played a very important role in start-up of the reactors (see Fig. 1). The recommended conditions for start-up of UAFB bioreactor were emperature 32–34 °C, pH 6.5–7.5, HRT more than 24 h, recycle ratio 2–10, nutrient required ratio (COD:N:P) 350:7:1, concentration of volatile fatty acids less than 1000 mg/L, pH adjustment with CaO, NaHCO3, and NaOH, MLVSS at initial sludge 15,000–20,000 mg/L, and volume of sludge required was 50–70% of the volume bioreactor (results not shown). The source anaerobic mixed culture was the same anaerobic wastewater treatment plant, or sludge taken from domestic anaerobic digester. The initial OLR was 0.5 kg/m3 d for start and increased to 2 kg/ m3 d after COD removal reached 50%. Similar observations have been reported by Pu.al et al. (2000) and Rao et al. (2004).
After the start-up under steady state conditions, bioreactors were kept at 32–34 °C, hydraulic retention time of 20 h, influent COD of 2000–8000 mg/L, and recycle ratio was 2.
Similar optimum conditions of the anaerobic Filter were found to be at an HRT of 24 h and temperature 35 °C by Kang et al. (2003).
Once the bioreactors were under steady state, the loading rate increased to 7.8 kg COD/m3 d for 40 days and another increase in loading rate up to 9.6 kg COD/m3 d for the next 40 days. The reason for selecting such values was to produce a synthetic wastewater similar to real effluents of sugar mills active in Iran. The first observation was based on the pH change of the effluents of the bioreactors. It appeared that anaerobic bio-Filters could be well adjusted to pH and neutralised the weak acidic feed. The main reason for acidic condition of the feed was due to anaerobic condition prevailing within the feed tank, and due to conversion of sugars to acids. As depicted in Fig. 1, the reactors were capable to adjust the pH without any meaningful difference. During this period no chemicals were used for pH adjustment although the alkalinity used in the feed would naturally contribute to this effect.
During the first period of 40 days, under OLR of 7.8kgCOD/m3 day, the reactor B1 produced higher removal rates compared to reactors B2 and B3. Fig. 2 showed that during the first period reactors were improving in terms of organic removal. However reactor B1 appeared to be more stable than other reactors. It was also experienced that 40 days were not sufficient for reactors to reach on full performance. Increasing the feed concentration to 8000 mg/L that corresponded to organic loading rating of 9.6 kg COD/m3 day, increased the efficiency of COD removal. The main reason could be the build up of biomass within the reactors. Although higher concentrations of biomass could increase the efficiency of removal but it could cause clogging in packed bed type reactors. This phenomenon has been expressed as a disadvantage of anaerobic bio-Filters. However, in this study no clogging was observed and no change in flow patterns were seen.
At higher OLR loading, the performance of reactor B1 was superior to B2 and B3, whilst B2 was producing effluents with lower quality in comparison to others. It becomes clear that surface area as well as the material of packing could have some effect on the build-up of biomass in bioreactors. The first part of the reactor, lowest 50 cm was more effective in terms of organic removal mainly due to higher concentration of biomass within this volume of the reactor. It is also found that reactor height may not be effective as it was originally assumed (Fig. 3). The experimental conditions were: pH 6.9, alkalinity 2300 mg CaCO3/L and OLR influent 9.6kgCOD/m3 d. However, increasing the feed concentration for development of active biomass in deeper parts of the bioreactor could cause clogging situation to develop.
To verify these facts samples of the packing were taken from different heights of the bioreactor B1. Fig. 3 shows the VSS related to concentration of the biomass at different heights of the reactor. It should be noted that since the reactor was up-flow, meaning that the feed was introduced at the bottom of the reactor, biomass agglomeration took place at the lower parts where the feed was strongest (Alkalay et al., 1997). It is generally understood that upflow bio-Filters are more efficient than down flow bio-Filters (Jawed and Tare, 2000). This fact could be as a result of different hydraulic conditions in the bio-Filters.
The results showed that bio-Filters could play a major role in the treatment of concentrated industrial effluents, such as sugar refinery wastewaters. Treatment efficiencies of 90% and above, in terms of COD, could be achieved by using an appropriate packing. The bio-Filter could tolerate very high organic loading in the order of 10 kg COD/m3 d with out any problem in the operation. For packing polypropylene pall rings appeared to be most stable than the other two bio-Filters. Although gas production was not measured with accuracy during the experimentation, it was clear that the bio-Filters produced biogas as expected in all conventional anaerobic systems.
This work was supported by Water and Environment Group (Isfahan high education and research institute) and BBRC (Sharif University of technology, Tehran, Iran). Authors are thankful to Sumit Kumar (V.V.P. Engineering College, Saurashtra University, Rajkot, India) for his help.
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