Developments in wastewater treatment in the meat processing industry: A review
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Bioresource Technology 54 (1995) 203-216 1996 Elsevier Science Limited
Printed in Great Britain. All rights reserved 0960-8524/96 $9.50 + 0.00
DEVELOPMENTS IN WASTEWATER TREATMENT IN THE MEAT PROCESSING INDUSTRY: A REVIEW
M. R. Johns
Department of Chemical Engineering, The University of Queensland, Queensland 4072, Australia
(Received 24 August 1995; accepted 30 August 1995)
Abstract A review of progress in the treatment of wastewater from slaughterhouses is presented. Significant progress in issues such as nutrient removal and high-rate anae- robic treatment are highlighted. Nevertheless, few data concerning waste minimisation and source reduction in slaughterhouses, which offers the most cost-effective route to waste management in the industry, exist. The information presented enables a better understanding of the problems encountered with the effluent from the industry and common pitfalls with its treatment.
Key words: Slaughterhouse wastewater, wastewater treatment, minimisation, nutrients.
AC AF AFB AS AS-BNR
BNR BOD BPR (T)COD DAF DO HRT N O&O TP RO SBR SVI TDS TF TKN TSS UASB VSS
Anaerobic contact process Anaerobic filter Anaerobic fluidised-bed reactor Activated sludge Activated sludge-biological removal process Biological nutrient removal Biological oxygen demand (mg/l) Biological phosphorus removal (Total) chemical oxygen demand (mg/1) Dissolved air flotation Dissolved oxygen Hydraulic retention time Nitrogen concentration Oil and grease concentration Total phosphorus concentration Reverse osmosis Sequencing batch reactor Sludge volume index Total dissolved solids concentration Trickling filter Total Kjeldahl nitrogen concentration Total suspended solids concentration Upflow anaerobic sludge-blanket reactor Volatile suspended solids concentration
The meat processing industry is large, common to many countries and generates large volumes of wastewater, which requires considerable treatment if its release to the environment is to be sustainable. Although a number of reviews have been published on the topic (Reczey, 1984; Cimino, 1987), the latest in English was that of Bull et al. (1982). In the intervening period there have been substantial fundamental and technical advances in generic pol- lution control issues, such as nutrient removal, high-rate anaerobic technology development and water reuse. This review attempts to identify the latest trends in waste management and treatment technology in the meat process industry and to dis- cuss the design and performance data available in the scientific public domain.
Characterisation of wastewater from slaughterhouses and rendering plants The concentrations of pollutants in various waste- water streams from slaughterhouses or rendering plants are summarised in Table 1. Despite the sub- stantial variation in the results, these data provide a useful guideline for wastewater-treatment-system design and act as a starting point for waste mini- misation. Whereas the combined slaughterhouse wastewater can vary substantially with respect to COD and TP content, the nitrogen content is usually more invariable.
Tritt and Schuchardt (1992) present the most recent and comprehensive summary of the physi- cochemical characteristics of many different waste streams from German slaughterhouses, but care is needed in using these figures. German slaughter- houses have no rendering plant, since this processing must, by law, be performed in a separate off-site facility (Tritt & Schuchardt, 1992). The data of Ste- bor et al. (1990) are derived from a very large, integrated US beef slaughterhouse and show excel- lent similarities with Australian data. For sheep-processing plants, the presence of a fellmong-
204 M. R. Johns
Table 1. Reported analyses of important wastewater sources in slaughterhouses
Parameter 1 (m~)
2 3 4 5 6 7 (95%limits) (mean;
Cooker Blood condensate (5,8) (8)
BOD 710-4633 490-650
TCOD 1925-11 118 1500-2200
SCOD 780-10 090 O&G 50-100
TKN 110-240 120-180
NH4 - N Tot P (PO43-) 13-22 12-20 VFA SO4- S Alkalinity
2105 1600-3000 1000-3500 (453) 5113 4200-8500 1400-5000 (1036)
1100-1600 897 100-200 (376) 1774 1300-3400 (357) 248 114-148 250-700 (44.7)
65-87 200-300 22.1 (4.5) 20-30 (1.5-2.5) 80-120
1900; 530-4 700
640; 220-2100 6000
115; 40-230 550 430-740 16,500
30; 3-70 150 430-740 3500 15; 6-34 50
Developments in wastewater treatment in meat processing 205
& Russell, 1988), since the condensed rendering vapours are the major pollution load. These are high in BOD and nitrogen concentrations, largely as ammonia, but poor in phosphorus, in contrast to slaughterhouse wastewater (Frose & Kayser, 1985). The ammonia nitrogen concentration may vary signi- ficantly between winter and summer, due to the more extensive degradation of raw material in sum- mer, which boosts levels of ammonia nitrogen.
WASTE MINIMISATION AND CLEANER TECHNOLOGY
A focus of modem waste management practice is the minimisation of process inputs. Slaughterhouses generate large wastewater volumes and are fre- quently inefficient users of water. Water consumption for slaughterhouses is reported by several authors (Table 4). Typical water consump- tion varies considerably. The typical minimum water usage figures worldwide appear to be 1.3-2.5 m3/ beast for beef slaughtering plants, assuming an average live weight of 0.5 tonne/beast in the US and Germany. Most recent Australian slaughterhouses have been designed on the basis of 1.5 m3/head water use, but actual industry use is considerably more. Figures for sheep are not quoted.
Typically, the wastewater generated comprises 80% of the fresh water input. No breakdowns of wastewater flow from specific process operations are published, but the major wastewater flows come from rendering, paunch processing and stockyard areas of the slaughterhouse. Considerable effort in the last decade has been directed at plant automa- tion. It is not clear whether the incorporation of these technologies into meat processing will reduce water consumption.
Schultheisz and Karpati (1984) summarise tech- nology improvements relating to water use and waste minimisation in the US up to 1977. The trend is clearly towards the choice of processes which reduce waste quantity and strength, particularly improved blood recovery, dry paunch dumping and regulated water use. Unfortunately, more recent sur- veys are not available. The emergence of
low-temperature edible-rendering systems has been especially constrained by the very strong wastewater generated (Cooper & Russell, 1988).
Many schemes are already implemented in slaugh- terhouses for the reuse of water for non-potable uses within the plant. Most of these involve no treat- ment of the water prior to its reuse. Kane & Osantowski (1981) described a pilot-plant study in which treated wastewater was passed through chemi- cal flocculation/clarification and dual media filtration prior to further upgrading by either ion exchange, reverse osmosis (RO) or electrodialysis. All the latter three processes achieved greater than 90% reduction of TDS, however, the use of RO was the most economic, with estimated capital and oper- ating costs for a 3.8 M1/day (1 MGD) system being at most 40 and 68%, respectively, of those of the other two processes. Furthermore, it required only half the space. It is not known whether the system has been installed at full scale.
Consideration and demonstration of the technical feasibility of the reuse of municipal wastewater as potable water has occurred in South Africa (Kfir & Slabbert, 1991) and several US cities (Rogers & Lauer, 1991). The safety and public health issues involved have been widely discussed, but generally pipe-to-pipe potable reuse is not favoured and most schemes in use involve a natural intermediate step (i.e. underground aquifer, reservoir). There are no reports of technology development or trials for the rehabilitation of treated wastewater from slaughter- houses for potable reuse.
New or even improved ideas for the recovery of valuable byproducts from slaughterhouse or render- ing plant wastewaters have received little attention, except for high-quality water, protein, biogas and struvite fertiliser. This may reflect the fact that the industry is, in fact, highly efficient in achieving product recovery prior to wastewater discharge.
Screening, settling and dissolved air flotation (DAF) remain widely used for the removal of suspended solids and fats, oils and greases from slaughterhouse
Table 4. Water consumption and effluent volume in slaughterhouses
Reference Nation Water use (m3/head) (m3/tonne live weight)
Schultheisz & Karpati (1984) Schultheisz & Karpati (1984) Stebor et al. (1990) Hopwood (1977) Jorgensen (1979) Schultheisz & Karpati (1984) Tritt & Schuchardt (1992) Metzner & Temper (1990)
US slaughterhouses 2.1-8.3 4-2-16.7 US meat packing 3.2-14.6 6.3-29.2 US Beef slaughterhouse (265/h) 1-3 a 2.6 a UK slaughterhouses < 2.5-7-5 < 5-15 Europe 2"5-5 5-10 Hungary 1-1.9 2-3-8 Germany 0.4-3.1 a 0-8-6.2 a Germany (rendering) only - - 1-25 ~
a _ Effluent production.
206 M. R. Johns
wastewater. Earlier studies of processes such as elec- tro flotation or ion exchange (Bull et al., 1982) to replace DAF systems have not proceeded further, suggesting inherent technical difficulties or unfavourable economics of these systems in practice.
The late 1970s saw the introduction of large dis- solved air flotation (DAF) units fitted with chemical precipitation into Europe, New Zealand and the US for protein recovery from wastewater. These pro- cesses gave 75-80% BOD5 reduction (Hopwood, 1977) and had the additional advantage of removing large quantities of nitrogen and phosphorus. Most systems, however, had considerable operating prob- lems, including long retention times and low surface-overflow rate, which led to solids settling, large volumes of putrefactive and bulky sludge (typi- cally 0.8-1.2 kg dry sludge/kg BOD5 removed), sensitivity of the system to flow variation and diffi- culties in sludge dewatering (Stebor et al., 1990). Furthermore, the protein product could not be readily sold and most have been shut down (Camp- bell, personal communication; Dague et al., 1990). The installation of new systems has not been reported in recent literature.
Several studies have investigated ways of enhanc- ing DAF operation on slaughterhouse wastewater. Travers and Lovett (1985) reported that optimum fat removal from slaughterhouse wastewater using DAF treatment without chemical addition is obtained at pH 4.0-4.5 (Table 5). However, the pH of slaughterhouse wastewater is rarely adjusted. Sub- stantially improved recoveries of fat and solids can be obtained using chemical addition (Green et al., 1981), which is more commonly practised in the US than Australia (Table 5). Large quantities of unstable sludge are obtained, however.
Steiner and Gec (1992) report that the introduc- tion of hydrogen peroxide into grease traps and DAF units can significantly enhance performance for O&G removal, largely through the nucleation of very fine oxygen bubbles. It appears that where chemicals are added to DAFs, the use of hydrogen peroxide may benefit the process. In contrast, Tra- vers and Lovett (1985) found the use of carbon dioxide and carbon dioxide/nitrogen gas mixtures instead of air for DAF systems treating slaughter- house wastewater gave little improvement in removal efficiencies, probably because of the extra turbulence found in the separating vessel using CO2
and larger bubble sizes, which depend on the gas used.
An interesting technology recently tested in Aus- tralia for fat and protein removal has been foam flotation, which has historically been used in the mineral industry (Jameson flotation cell). Bremmell et al. (1994) describe the use of foam flotation to reduce BOD by 70% and fats by 6-fold in dairy wastewater. The wastewater is chemically floccu- lated, followed by foam flotation using an induced flotation cell. The technology has not been applied to slaughterhouse effluent, but looks promising.
ISSUES IN OVERALL WASTEWATER SYSTEM DESIGN
Post-primary treatment of slaughterhouse waste- water depends on the location. In Europe, most slaughterhouses and rendering plants deliver their wastewater to municipal systems after preliminary primary treatment (Sayed et al., 1987). Where this is not feasible, some plants have installed activated- sludge plants with biological nutrient removal. In the US, the situation is unclear, although there seems to have been a trend towards activated-sludge plants. In the majority of Australian slaughterhouses, waste- water has passed through anaerobic treatment ponds then into aerobic-pond systems. In a few, direct aerobic treatment (i.e. activated sludge) has been used. The goal of the former has been to achieve BOD reduction, whereas the goal of the latter has often also included nitrification. In contrast, New Zealand slaughterhouses often irrigate primary- treated or anaerobic-treated wastewater directly to land.
TRENDS IN ANAEROBIC SYSTEMS
Anaerobic systems are well suited to the treatment of slaughterhouse wastewater. They achieve a high degree of BOD removal at a significantly lower cost than comparable aerobic systems and generate a smaller quantity of highly stabilised, and more easily dewatered, sludge. Furthermore, the methane-rich gas which is generated can be captured for use as a fuel.
In most countries, the anaerobic pond has been used to achieve a high reduction in BOD, oil and
Table 5. DAF performance on slaughterhouse wastewater
Treatment Mean removal efficiency (%) Reference COD TSS O&G
Air 40 60 90 Travers & Lovett (1985) Acid, pH 4-4.5 71 78 93 Travers & Lovett (1985) DAF and chem. 32-92 (BOD) 70-97 89-98 Karpati & Szabo (1984)
Developments in wastewater treatment in meat processing 207
grease and suspended solids concentrations from the primary-treated slaughterhouse wastewater prior to subsequent aerobic treatment. Unfortunately, the propensity for odour generation from anaerobic ponds has threatened their continued use in many areas. Consequently, new developments in anaerobic technology during the last 15 years are of consider- able interest. These can be divided into two groups:
(i) covered anaerobic ponds, (ii) high rate anaerobic systems.
Covered anaerobic ponds In the past decade, synthetic floating covers on anaerobic ponds have been installed worldwide to trap odour and biogas (Dague et al., 1990; Safley & Westerman, 1992). These systems occupy a niche between existing anaerobic ponds on the one hand and the more sophisticated high-rate anaerobic sys- tems on the other. Compared to traditional, uncovered anaerobic ponds, covered ponds offer the performance of the former, but reduce odour releas...