1 Introduction

The worldwide production of meat doubled folded in the past three decades (Bustillo-Lecompte and Mehrvar, 2015), expected to replicate the progress of meat production up until 2050. Moreover, In India, beef production has been growing due to increased income and the shift toward a western-like protein-rich diet. Meat is a significant source of protein and a valuable commodity; it is only available at roughly 15 g/person/day, despite the Indian Council of medical research (ICMR) recommendation of 30 g/person/day (Islam et al., 2016). A brief note on slaughterhouses, they are facilities where animals are slaughtered for consumption as food locally and abroad (Hilares et al., 2021). There are approximately 3600 registered slaughterhouses in India, with 56 of them located in the state of Uttar Pradesh alone. All the major Indian cities have central slaughterhouses that date back to the British period (>70 years old) (Singh et al., 2014). Among them, Uttar Pradesh is the highest producer of meat products with a 19.1% share in the state, which produced around 7.515*103 tonnes of buffalo meat. The data from the state’s animal husbandry department shows that in the year 2014–15, industrial and structural slaughterhouse improvements have been highly subsidized, which has contributed to the sector’s growth. The Uttar Pradesh meat processing industry accounts for 50% of India’s exports, which makes it one of the leading meat producers and exporters in the country (Meiramkulova et al., 2020). The procedure of treatment, management, and disposal or recycling of organic solid and liquid wastes generated from slaughterhouses are intimidating works because of the massive volumes of waste material generated every day in solid and liquid forms (Ahmad et al., 2014).

The meat processing wastes have high carbon-based and inorganic compositions (Xiang et al., 2019). The high suspended solids content, the dark color, and the offensive odor are responsible for poor bacteriological standards (Martínez et al., 1995). The waste from slaughterhouses contains high-strength complex wastewater with about 45% soluble and 55% abrasive suspended organics. The organics originate from blood and offal (Ahmad et al., 2014). The lion's share of the uncleanness is produced by the blood and by intestinal and abdominal secretions. Additionally, Organics, pathogenic and non-pathogenic bacteria, and cleaning detergents and disinfectants are all found in high concentrations in slaughterhouse wastewater (SWW) (Kreutz et al., 2014). Nutrients, heavy metals, color, and turbidity are also present. Moreover, disinfectants, cleaning chemicals, and veterinary medications can be found. Preliminary treatment of SWW can include grit chambers, screens, settling tanks, and dissolved air floatation (DAF) systems, which are widely utilized before biological processes. The removal of suspended solids, oil, and grease is required to avoid sludge flotation, and components overload (Johns, 1995; Massé and Masse, 2000; Wang and Banks, 2003; Sayed and de Zeeuw, 1988; Lettinga and Hulshoff Pol, 1991; Petruy and Lettinga 1997; Halalsheh et al., 2005). Subsequently, the SWW flow is intermittent, and an equalization tank is compulsory to reduce the consistency variations and the carbon-based load. As an initial biological treatment, most abattoir wastewater treatment plants (WWTP) use activated sludge processes, stabilization ponds, and anaerobic reactors (Vilvert et al., 2020). The high demand for energy for aeration and the extensive generated sludge increase the operating expenses of the treatment system (Gude, 2015). Consequently, aerobic biological treatment is not recommended for use on high-strength industrial wastes by experts (Del Pozo et al., 2000; Parawira et al., 2005). Energy can be reserved, and sludge production can be decreased by anaerobic digestion of the SWW (Rasapoor et al., 2020). The typical limits of discharge of slaughterhouse wastewater for COD, BOD, and SS are 250 mg/l, 30 mg/l, and 50 mg/l, respectively. The efficient performance of the treatment system is the most critical factor that directly impacts the cost, treatment, and disposal of wastewater (Lyu et al., 2020). This research aims to evaluate the performance and examine the factors that improve the quality of slaughterhouse effluent treatment plants (SETP). In addition, the work will suggest solutions to provide stable and efficient operation of full-scale SETP.

2 Materials and methods

The study was conducted at a SETP of 800 m³/day in Aligarh, Uttar Pradesh, India. The SETP consisted of static screens, an oil skimmer, an equalization tank, a DAF system, an up-flow anaerobic sludge blanket (UASB) reactor, followed with two activated sludge processes (Fig. 1). The coarse screen removed solids larger than 20 mm, and the fine screen removed solids larger than 5 mm. Before entering the DAF unit, 30% effluent was recycled and mixed with the liquid fraction of the blood that passes through the static screens, and then coagulation was homogenously mixed in a 175 m³ equalization tank. The waste water after passing through the skimming tank, it goes into the alum dosing tank where coagulation and flocculation leads to the settlement of pollutants and the effulent of alum tank goes to the equalization tank. The rectangular 857 m³ UASB reactor with 33% recycling was constructed after the DAF unit. Furthermore, Aeration Tank −1 and Aeration Tank −2 of volumes 321 m³ and 412 m³, respectively, with 40% recycled effluent. Followed by clarifier-1 and clarifier-2 of volumes 101 m³ and 171 m³, respectively.

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Fig. 1

Simplified layout of the SETP: 1, 2, 3, 4 and 5 are the sample collection points.

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The pH was controlled in the biological systems by adding an alkalinity buffer in the influent of the reactors. The hydraulic retention time (HRT) of the effluent varied from 10 to 15 h daily, rendering to the work managing. The design and operating parameters are listed in Table 1 for the DAF unit, UASB reactor, aeration tanks, and secondary clarifiers.

Influent samples of the SETP followed by effluent of different treatment units have been collected onsite wastewater treatment plant throughout the employed hours. The average calves slaughtered on each day are 500 heads. Slaughtering process wastewater samples from different units were collected on 3 alternate days each week over a period of 17 weeks i.e. 2nd January 2017 to 1 May 2017, between 10 a.m. and 1 p.m. Samples in bottle were stored in deep freezer in the lab for analysis on the same day.

Acidity (pH), total suspended solids (TSS), biological oxygen demand (BOD), and chemical oxygen demand were all measured in samples collected from various locations (COD). All of the tests were carried out using the following standard procedure for water and wastewater testing.

The acidity (pH): After standardizing the instrument at pH 4 and 7 with the calibration solution of pH 4 and 7, the collective movable meter (Type HI 8424) was used for testing.

The biochemical Oxygen Demand (BOD): The samples were incubated at 20 °C for 5 days using the OxiTop measurement device. Following mixing, the samples were placed into OxiTop bottles and diluted to the machine's test range as recommended by the manufacturer's instructions.

The chemical oxygen demand (COD): Chemical oxygen demand is measured to determine the total oxygen required to oxidise the complex organic matter content of a sample by strong oxidants (2KCrO₂ 27/H₂SO₄ at 145 °C) due to the multifaceted content of the slaughterhouse's wastewater and the presence of uneasy biodegradable organic matter.

3 Results and discussion

3.2

3.2 Performance of the effluent treatment plant (SETP)

The purpose of installing the DAF unit before the UASB reactor was to adapt wastewater to the UASB process. COD, BOD, and SS removal efficiencies in the DAF unit were 29%, 28.58%, and 71.13%, respectively (Fig. 2), screening differences in the unit’s routine over the operating period (Table 3). In the pre-treatment food industry, chemical-DAF units remove SS ranging between 80 and 99% (Woodap et al., 1977; Ho and Tan, 1989; Rusten et al., 1990; Schneider et al., 1995; Núñez et al., 1999; Azbar and Yonar, 2004; Alam et al., 2021; Akhtar et al., 2019; Akhtar et al., 2021). Adjusting the operating condition and chemical treatments can improve the instability of dissolved air floatation effluent quality. Industrial process management can also help in improving the further efficiency.

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Fig. 2

Parameter monitoring of the DAF unit during the study period. (a) COD, (b) BOD and (c) TSS. ‘—’ represents Chemical-DAF removal efficiency, ‘●’ denotes DAF effluent.

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Table 3 Physiochemical monitoring parameters of the slaughterhouse Effluent Treatment System from January 2017 to May 2017.

Parameter	Na	Industrial Effluent				Unit effluent				Removal efficiency (%)
		Average	Min	Max		Average	Min	Max		Average	Min	Max
DAF
COD BOD TSS pH	41 41 41 41	6172 ± 528 4009 ± 436 2813 ± 182 6.8	2835 1860 1252 4.3	13,950 9062 5615 7.6		4380 ± 238 2863 ± 145 834 ± 90 7.2	2170 1405 125 6.6	11,596 7538 2500 7.5		29 ± 5 28.58 ± 6.2 71.13 ± 7 –	3.2 3.6 55.48 –	68 62 90 –
UASBR
COD BOD TSS pH	41 41 41 41					3414 ± 460 2380 ± 319 521 ± 175 7.2	1020 690 113 6.8	7320 4826 1754 7.7		22 ± 8 16.86 ± 7.5 37.57 ± 4 –	1.36 1.76 1.79 –	58 54.90 75.56 –
Clarifier-1
COD BOD TSS pH	41 41 41 41					2519 ± 117 1720 ± 234 371 ± 109 7.5	390 273 92 7.1	5225 3611 925 8		26 ± 3 27.7 ± 5 28.6 ± 2 –	2.96 2.16 1.52 –	62 60.43 60.12 –
Clarifier-2
COD BOD TSS pH	41 41 41 41					1559 ± 212 930 ± 163 285 ± 95 7.5	234 95 69 6.4	3523 2533 749 8.4		38 ± 6 45.8 ± 4 23.12 ± 3.8 –	8.77 10.27 3.23 –	77 85.43 65.06 –

The adequate performance and stability of the reactors made adopting the UASB process as a fundamental technology at the WWTP unsatisfactory (Table 3). COD removals efficiency of UASB reactor showing poor performance. Similar results were also observed in the removal efficiency of BOD and TSS of UASB reactors treating slaughterhouse wastewater. Over the study period, very little improvement in the removal efficiency of COD and BOD of the UASB reactor was achieved (Fig. 3). Furthermore, the results of TSS removal efficiency of the reactor decreased with time.

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Fig. 3

Monitoring parameter of the UASB during the study period. (a) COD, (b) BOD and (c) TSS. ‘—’ represents UASB removal efficiency, ‘●’ denotes UASB effluent.

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The Suspended Growth Activated Sludge process, Aerobic system-2 shows better results in removal of the COD and BOD as reported in Table 3 and Figs. 4 and 5. The performance was affected by poor performance of the UASB. Moreover, dissolved oxygen was found to be less than 1 mg/l in Aeration tank-1 and Aeration tan-2 on an average, may also be the reason for inadequate performance. The maximum 95% of COD removal can be obtained with 40% of sludge return, HRT 8 h, DO 3.5 mg/l and pH stable at 7.65 with the sludge aged and the bio solids retention time 23 days (Ebrahimi and Najafpour 2016).

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Fig. 4

Monitoring parameter of the Clarifier-1 during the study period, (a) COD, (b) BOD and (c) TSS. ‘—’ represents Clarifier-1 removal efficiency, ‘●’ denotes Clarifier-1 effluent.

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Fig. 5

Monitoring parameter of the Clarifier-2 during the study period. ‘—’ represents Clarifier-2 TSS removal efficiency, ‘●’ denotes Clarifier-2 effluent TSS.

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Overall performance of wastewater handling plant was assessed rendering to the value of monitoring limits. The Average COD, BOD, and TSS removal efficiency of SETP was found to be 74.7 ± 1%, 76.8 ± 1%, and 90.14 ± 1% (Table 3, Fig. 6). In Table 2, the average COD, BOD, and TSS of wastewater from the industrial slaughtering process are given along with the minimum and maximum values of Industrial effluent during the study period. A graphical presentation of the overall performance of the SETP is given in Fig. 6 for the COD-total, BOD-total, and TSS.

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Fig. 6

Parameter monitoring of the SETP during the study period. (a) COD, (b) BOD and (c) TSS. ‘—’ represents SETP removal efficiency, ‘●’ denotes SETP effluent.

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4 Conclusions

The DAF is showing considerably good performance; however, it can be further enhanced by taking some corrective measures in pretreatment. UASB reactor showing poor performance. The imperfect performance of the reactor hence resulting in inadequate performance of the Activated Sludge Process (ASP). For the efficient performance of the SETP; i) Proper pretreatment has to be installed and the existing units needs to be rectified. ii) It has been proposed to install a drum screen for removing dung. iii) The industry should have two dung separators. iv) Oil skimmer needs to be rectified. v) UASB needs commissioning again and the excessive sludge needs to be drained. vi) New high-power aeration system should be installed which to improve the performance of the aeration systems. vii) The company should install tertiary treatment which is essential to reduce the concentration of the pollutants to the desired limit.