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VIETNAM JOURNAL OF CHEMISTRY VOL 51(2) 264 278 APRIL 2013 OPTIMIZATION OF FISH PROCESSING WASTEWATER TREATMENT TECHNOLOGY FOR ENERGY RECOVERY N Trautmann''''*, D C Chinh^ T T Long^*, K H Rosenwinkel'''' ''''in[.]
VIETNAM JOURNAL OF CHEMISTRY VOL 51(2) 264-278 APRIL 2013 OPTIMIZATION OF FISH PROCESSING WASTEWATER TREATMENT TECHNOLOGY FOR ENERGY RECOVERY N Trautmann'*, D C Chinh^ T T Long^*, K -H Rosenwinkel' 'institute of Sanitary Engineering and Waste Management, Leibniz University of Hanover Germany ^Southern Institute for Water Resources Research, Ho Chi Minh City, Vietnam Received 19 September 2012 Abstract The strong economic growth in South-East Asia leads to increasing discharge of wastewaters and an increasing energy consumption The fish processing industry is one of the fastest growing branches with huge amounts of organically polluted wastewaters To face this issue, in the present work an optimized system for the treatment of wastewater from fish processing factories is developed In the first step, the state of art for treating fish processing effluents is described to give an overview ofthe experiences in this field Based on anaerobic batch tests the anaerobic degradability of COD from these effluents were determined and found to be 75-80% for grease and wastewater from one part-stream With the combination of on-site flotation units with a centralized anaerobic digestor for flotahon tailings an energy recovery rate of kWh/per ton raw fish processed can be achieved This value does not include the energy consumption during operation ofthe treatment system Keywords: Anaerob, treatment, Vietnam, fish industry INTRODUCTION In the last few years, South-East Asia has experienced sfrong economic growth leading to an increasing number of industrial zones and higher demand for energy This frend is supported by the policies opted for, as the armouncement of the implementation of 90 new Indusfrial Zones (IZs) by 2015 shows (Vietiiam News 2010) The growth rate of energy consumption is more than 11% p.a in Vietiiam alone (APC 2008) Along with this higher energy consumption, increasing mdustrial production has a severe environmental impact (pollution of water bodies, greenhouse gas emissions) Furthermore, the implementation of stnct discharge limitations emphasizes the need for sustainable wastewater freatment Regarding adequate freatinent of the wastewater from industiial zones, there is a special lack of appropriate technologies for an efficient integrated system for freatinent and energy recovery purposes The recent development in the indusfrial production in Vietiiam showed, that also high-level technologies can be handled under local conditions As the freatment of industrial waste water is under the industry's responsibility, it is feasible to apply advanced freatment concepts In a joint Vietnamese-German research project funded by the Federal German Ministry of Education and Research (BMBF) and the Vietnamese Ministry of Science and Technology (MOST) called AKIZ, such a system for die freatment of wastewater from the fish- and seafoodprocessing industry is to be developed and evaluated Fig 1: Fish production in Vietiiam since 1974 (FAO 2012 The focus of one sub-project is the development of a sustainable method of freating wastewater from the fish-processing industiy This branch of industiy is die third largest industiy in Vietiiam and it has 264 VJC, VoL 51(2), 2013 experienced enormous growth in the last few years, as is shown in Fig In 2008 the total quantity of rawfishprocessed was more than 4.5 million tonnes (FAO 2010) These enormous quantities show the high degree of potential pollution that unfreated wastewater discharges from fish factories into water bodies can be expected to generate Taking into consideration the growing demand for energy for the industrial sector in general and for wastewater treatment in particular, new energy-efficient freatment systems have to be developed State of the art In the last few decades several investigations have been carried out on the treatment of wastewater from fish industries Various biological systems have been implemented to provide major freatment facilities, e.g activated sludge systems, UASB systems, rotating disk reactors, frickling filters and lagoons (Chowdhuiy et al 2010) Due lo high COD concentrations in raw wastewater, research and practical technology (e.g Palenzuela-Rollon et al 2002, Veiga et al 1994) both focus on the use of anaerobic treatment steps But as anaerobic systems don't remove nifrogen to a significant extent, it might be necessary to apply further freatment Pre-ireaiment The elimination of suspended solids, oil and grease from fish factories' wastewater can be achieved through dissolved air flotation (DAF), as Genovese et al (1995) and Steinke and Barjenbruch (2010) have shown This results in the removal of organic nifrogen and COD at efficiencies of up to 36% and 56%, respectively (Steinke and Baijenbnich 2010) The volume-specific energy input required for DAF ranges from 0.08 kWh/m^ to 0.125 kWh/m^ according to Stark et al (2008) and Bennoit and Schuster (2001) Anaerobic treatment Anaerobic treatment is a suitable process for COD removal from fishprocessing wastewater, as vanous examples in Chowdhury et al (2010) show Although high sodium concenfrations can be inhibiting to anaerobic processes (Levebvre 2006), the latter list various examples showing that adaptation to high salinity is possible (e.g Omil 1996, Boadman 1994 and Xia 2010) The energy input required is much less than for aerobic freatinent as no aeration is necessary Furthermore energy is recovered through biogas usage, According to Palenzuela-Rolon et al (2002) it is necessary to eliminate most of the lipid load to permit a stable anaerobic freatment process with Trinh Thi Long, et al high-rate reactors (e.g UASB) The energy consumption for pumping and for stirring can be assumed to be 0.005 kWh/(m^*mhc,ghi) and 0.12 kWh/(m^reaciorvoiumc*d), respcctivcly (Urban 2009) Heating can be neglected, because the wastewater temperature is sufficient owing to the climatic conditions in fropical regions Methane (CH,) production is 0.35 m'/kg of CODdegraded with a net calorific value of 10 kWh/m' CH4 under standard conditions Tlie final energy output depends on the chosen technology for energy usage Activated sludge systems Conventional aerobic carbon and nifrogen removal systems are an appropriate technology for the complete freatment of wastewater produced by the fish-processing industry Examples of its application can be found in Chowdhury (2010) and Steinke and Barjenbruch (2010) The energy consumption of nifrogen removal by nifrification/denitrification is 3.7 kWh/kg N (Beier et al 2008) This value refers to systems to which no extemal carbon source has to be added, to compensate a lack of COD in the wastewater sfream For denitrification reactors (stirring only) the energy demand is approx 0.5 kWh/m^ (Beier et al 2008) MATERIALS AND METHODS 2.1 Waste Water Characteristics In the fish processing factory the waste water from the skirming and filet section of the process, the grease from the separators and the influent to the decentralized wastewater freatment plant (WWTP) have been monitored The results are listed in table The influent to the WWTP shows lower values, because the high-polluted part-sfream is diluted with water from washing areas and others Table 1: Wastewater from fish processing Code [mg/l] COD TSS VSS Skinning/Filet Section 4.500 InHuentWWTP 1.130 720 547 [g/g] [g/g] [%] 1.56 435 98 Grease/proteins from Separator 3.760 TN 2.170 260 101 Based on the production data the specific loads have been calculated as seen in table whereas 90% J VJCVol 51(2), 2013 Optimization of fish processing wastewater ofthe COD load derives from the skinning and filet section Table 3: hiput of anaerobic batch tests Test Waste Water Fish Processing Flotation tailings srease/proteins Seeding Sludge Brewery UASB Seeding Sludge Municipal Digestor 2.2 Batch Device Set-Up The AMPTS system consists of parts, namely the sample incubation unit, CO2 fixing unit, flow cell array unit and the software The sample incubation unit consists ofa water bath with 15 places to keep the 500ml reactors The reactors consist of a stirrer as well, which can be adjusted with the software Each reactor has two gas ports, one to flush the system with N2, which can be blinded after flushing and another port which collects the biogas produced to the next unit, called the CO; fixing unit CO2 fixing unit consists of 15 botdes with NaOH to absorb CO2 fraction in the biogas This CO2 fixing unit is kept on a magnetic stirrer to avoid the mass fransfer limitation and to avoid the over estimation of the biogas produced The third part, flow cell array unit is just like a tilting bucket to measure the biogas flow rate The gas measurement is taken every 23 mins, and stored in the computer through the software interface The schematic figure is given in figure COD TN 4.44 5.02 0.45 TP S04 0.12 0.14 VSS 4320 mg/l COD 3760 2170 246 mg/l TN 1560 g/kg 430 g/kg 98% 2.4 g/kg 64 g/l 49% J 26 68% RESULTS AND DISCUSSION To examine the general feasibility of anaerobic freatment of fish processing wastewater and its contents anaerobic batch tests has been executed In both tests, blank tests with sludge only have been added to the experimental set-up 3.1 Test 1: Methane potential of wastewater Table 2: Specific loads based on raw fish processed Q [mVt] SS An important influence factor for anaerobic degradation is the Sludge Loading Rate (SLR in g COD/g VSS) To avoid inhibition by waste water ingredients, different SLR have been tested As shown in Fig 3, the degradation rate in the first 1015 hours increases with increasing SLR from 0.16 to 0.62 g COD/g VSS (slope of the curves) Further increasing of SLR up to 0.95 g COD/g VSS did not lead to faster degradation For lower SLR a COD degradation efficiency of around 80% could be reached But it can be observed, that the methane production don't increase with the same amoimt as the COD input increases with higher SLR It can be assumed, that inhibiting substances in the wastewater (e.g free ammonia from hydrolyses of proteins, detergent) or intermediates (e.g acetic acid) effect the degradation and avoid a complete conversion to methane kg/t •"Pf lid 1- N2 lii!,hiii^ port 4- WuierbuUi 2- SiiiTLT molor usacnihly 5- C» >2 li.Miig ii Fig 2: Set-up ofthe AMPTS (Anaerobic Mobile Methane Potential Test System) Batch Test Input Higher COD concenfration in subfrate are favourable for anaerobic freatment Therefore high polluted fractions have been chosen for feasibility test with anaerobic batch tests The batch experiments have been executed in diff"erent locations, so two types of seeding sludge had to be chosen The input data are given in table 3.2 Test 2: Methane potential of flotation tailings In a second batch test the methane potential of floating suspended solids from waste water of a fish processing plant has been determined (widi SLR = 0.8 g COD/g VSS) The amount of input COD was 11.6 g The total biogas and methane production over time are shown in Fig The methane content after steady state was 266: VJC VoL 51(2), 2013 Trinh Thi Long, et al polluted part-sfreams from different fish processing factories are tieated to gain energy rich flotiition tailings These could be converted into biogas in a cenfralized anaerobic reactor, followed by a biogas utilization imit As the main energy consumption is caused by freezing and cooling of products and facilities, the application of absorption cooling machines could be favourable The low polluted part-sfreams and the pre-freated highly polluted part-sfreams will flow to den central WWTP 80% In literature it can be found that the theoretical methane content in biogas from anaerobic digesstion of grease ist up to 75% in the biogas The higher value may result from a not complete CO2absorption in the fixing unit Assuming a methane content of about 75%, the methane production would have been 3,11 With the specific methane production of 0.35 per g CODdegraded, a total amount of 8.75 g COD has been converted into methane This results in an COD conversion efficiency of 75% of the input COD and no sfrong inhibition could be observed After 20 days the methane production has amlost been completed M) t-f AO IV5 TO Fig 5: Concept for pre-freatment of fish processing wastewater Fig 3: Methane production from wastewater (without blank test methane production) A COD balance for the anaerobic pre-freatment ofthe wastewater from the skinning and filet process based on processed raw fish is shown in Fig As the main pollution in the specific waste water derives from suspended solids, a COD removal efficiency of 75% is assumed for flotation units With an anaerobic degradation efficiency of 75%, 56% ofthe influent COD is converted into methane Finally kWh per t raw fish can be generated The feasibility aside ftom technical issues depends on various (e.g economical) boundary conditions One key point could be die market price of grease from fish processing that is often sold for biofuel production For its application also nutrient removal in aerobic systems or water reuse in agriculture has to be considered Time |d) fig 4: Methane production from wastewater (without blank test methane production) 3.3 Optimized Treatment Concept for Fish Processing Wastewater The results from batch test show that both, direct freatment of wastewater and tailings from mechanical pre-freatment for grease separation could be used for energy recovery As the high grease content of die wastewater could lead to operational problems in direct anaerobic freatment, the digestion of the solid phase is favourable For an industiial zone widi cenfralized WWTP, where various fish processing plants are located a waste water freatment concept as shown in Fig is proposed hi decenfralized flotation units the highly CONCLUSION The executed batch tests show, that anaerobic treatinent of bodi, highly polluted wastewater and grease/proteins from separators is possible The specific sitiaation in Vietiiam, with a high density of fish processing plants in industiial zones, leads to a combined decentralized/cenfralized proposal for energy recovery from fish processing wastewater The proposal allows on-site freatinent of highly polluted part-sfreams to relieve cenfralized WWTP for industiial zones from COD loads 267 Optimization offish processing wastewater VJCVol 51(2), 2013 Raw WW COD - 100 % COD4.51 kflft Raw Flằh coo ã 25 % CODô 1.13 kg/t Flotation taillngi COD«7S%| CODS-3« hflft Bloga* COO-19%1 COD0,SS kgrt COD > H X COD2.S3 kg/t KWhrt Raw Flati Fig 6: COD Balance for anaerobic freatment with upsfream flotation Department [online] Rome [Cited 18 August 2010] F Omil R Mendez, J M Lema Anaerobic treatment of seafood processing waste water in an industrial anaerobic pilot plant Water SA, 22(2), 173-181(1996) A Palenzuela-Rollon, G Zeeman, H J Lubberding, G Lcttinga, G J Alacrts Treatment of fish REFERENCES processing wastewater in a one- or two-step upflow anaerobic sludge blanket (UASB) 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to thinkgreen, 17.05.2010 Corresponding author: Trinh Thi Long Southern Institute of Water Resources Research Ho Chi Minh City, Vi^t Nam Emad: nlongvn@gmaiLcom Corresponding author: Niklas Trautmann Listitute of Sanitary Engineering and Waste management Hanover, Germany Email: Trautinann@isah.uni-hannover.de