Introduction

Contemporary society must address and resolve numerous significant issues to sustain and enhance the quality of life, ranging from global water stress to the depletion of raw materials (Drioli et al. 2020). The three main issues of contemporary society are drinking water, food, and energy. According to numbers 2 and 6 of the 17 Sustainable Development Goals (SDGs) descried by the United Nations (UN), “Zero Hunger” and “Clean Water and Sanitation,” respectively. The demand for water resources, especially fresh water, is increasing as the global population grows (Feng et al. 2009; LEITAO et al. 2006). By 2025, the Food and Agriculture Organization of the United Nations expected that 1.8 billion people would live in countries or regions facing extreme water scarcity; the share of water per capita would be less than 500 cubic meters per year (Organisation for Economic Co-operation Development (OECD, 2020). Innovative approaches to water and wastewater management have emerged in response to the limited freshwater sources. Reusing treated wastewater gives the chance to use resources more sustainably (Bustillo-Lecompte and Mehrvar 2017). Therefore, the implementation of advanced wastewater treatment techniques is crucial.

The slaughterhouses have a significant sector of industry because the meat is an important part of the diet in many nations globally (Johns, 1995). The Organisation for Economic Co-operation and Development reported that the meat production around the world will increase to be 360 million tons by 2029 (LEITAO et al. 2006). The water demand for one ton of meat production on average is 15,500 m3 for cattle, 4800 m3 for pigs, 6100 m3 for sheep, and 4000 m3 for poultry (Hoekstra and Chapagain 2006).

The meat processing industry has the highest demand for fresh water (24%), compared to other food industries such as the beverage industry (13%) and the dairy industry (12%) (Bustillo-Lecompte and Mehrvar 2017; Compton et al. 2018). For every ton of produced meat, about 1.5 to 18 m3 have been discharged so that the meat industry has a considerable impact on the water balance in the world. In further depth, slaughtering cattle and pigs produced wastewater about 1.6 to 9 m3, while sheep produce about 5.5 to 8.3 m3 and poultry 5 to 15 m3 per ton [(OECD and FAO 2020)].

Slaughterhouse wastewater is high-strength wastewater with high concentrations of organics, as well as pathogenic and nonpathogenic microorganisms (Masse 2000). Table 1 summarizes the wastewater characteristics of slaughterhouses (SWW) in various countries worldwide.

Table 1 Slaughterhouses wastewater characteristic
Full size table

Table 2 describes the existing legislation and discharge limitations for organic substances and nutrients in the slaughterhouse wastewater (SWW) for a suitable discharge into the environment in various jurisdictions globally.

Table 2 Slaughterhouses wastewater discharge limitations
Full size table

Conventional treatment technologies for slaughterhouse wastewater (SWW) may not achieve the allowable limits after pretreatment. The most common technologies used are chemical coagulation and flocculation, clarification processes, and biological processes (Al-Mutairi 2006). This is one of the most common ways to treat wastewater, and it depends on how much MLSS is in the biological reactors (Nile et al. 2024). Alternative processes for wastewater treatments include electrocoagulation, advanced oxidation, and cold plasma (Yildirim et al. 2019; Kim et al. 2018a, b). Often used as a primary treatment method (Johns, 1995), the DAF system achieves removal efficiencies of 70% for chemical oxygen demand (COD), 70% for total phosphorus (TP), 55% for total nitrogen (TN), and 85% for fat oil and grease (FOG) (Rosenwinkel et al. 2020; UBA 2003). Using aluminum sulfate, ferric chloride, ferric sulfate, and aluminum chlorohydrate as coagulants to treat SWW results in removal ratios of TP, TN, and COD up to 99.90, 88.8, and 75%, respectively (Núñez et al. 1999). Recently, advanced wastewater treatment technologies have utilized the electrocoagulation (EC) process. It has been confirmed that EC technology has a significant efficiency of removing organics, nutrients, heavy metals, and even pathogens from SWW without adding chemicals. Up to 93% of COD removal (KOBYA et al. 2006), in addition, laboratory pilot-scale was used to evaluate the EC process for removing organic compounds from SWW, and the results deduced that the use of steel bipolar electrodes achieved high removal ratios of COD, BOD, TSS, turbidity, and oil grease removals of up to 84, 87, 93, 94, and 99%, respectively. Membrane technology is one of the alternative technologies used for SWW treatment. The RO process was examined as a secondary treatment for SWW; the results showed removal efficiency of COD 85.8%, BOD 50.0%, TP 97.5%, and TN 90.0% (Bohdziewicz and Sroka 2005; Caldera et al. 2005). On the other hand, the biological treatment is often used as a secondary treatment process to reduce the concentrations of BOD and COD by removing the soluble organic compounds. Aerobic and anaerobic treatments are used individually or combined depending on the SWW characteristics. A UASB pilot reactor with a volume 4.0 L was examined for 90 days and hydraulic retention time of 24 h. to treat SWW subjected to COD concentrations ranging from 1820 to 12,790 mg/l; the COD removal ratio was up to 94.31% (Caldera et al. 2005). Using a UASB reactor followed by anaerobic anoxic and oxidative (A2/O) treatment to treat SWW, the experiments proved that the suggested method achieved high removal efficiency of COD 97.31%, BOD 96.91%, TS 57.61%, TDS 47.91%, TSS 96.3%, NH4 73.11%, PO4 83.61%, and NO3 93.01% at HRTs values of 24 h for the UASB reactor, 12 h for the anoxic tank, 24 h for the aeration tank, and 3 h for the final settling tank (Saghir and Hajjar 2022). Horizontal-flow biofilm reactor (HFBR) subjected to two different organic loading rates of 0.53 and 1.3 kg COD/m2/d. Under steady-state operation conditions, the system archive removal ratios were 56, 85, 95, 50, and 56% of carbon, COD, nitrogen, and ammonia–nitrogen, respectively (Doma and elkammah, 2020). A pilot-scale model was conducted to investigate an anaerobic and coagulation–flocculation hybrid process. The results showed that implementing anaerobic treatment as the first step reduced the concentration of COD, TSS, and turbidity. Furthermore, by using an aluminum sulfate dose of 110 mg/l concentration of (TSS), turbidity, (COD), (TDS), and (EC) have been reduced up to 71, 41, 76, 49, and 52%, respectively (Zamani et al. 2019). One of the alternative processes used to overcome these problems of conventional treatment systems of SWW, utilizing the principle of adsorption, can be a highly effective solution. Because adsorption has a significant effect in wastewater treatment (Bamba et al. 2009; Sennaoui et al. 2015). Activated carbon is a very low-cost material. Activated carbon is an industrial adsorbent that consists of carbon materials with a permeable configuration and increased surface area (Asadullah et al. 2007; Yeganeh et al. 2006). Activated carbon has various characteristics, including high rate adsorption and porous structure (Sanni et al. 2017). Activated carbon is commonly used for reducing BOD and COD concentrations in wastewater (Ghodale and Kankal 2014). Sawdust is low in ash and high in carbon content (50% w/w) (Oladimeji et al. 2021). So that it is considered one of the activated carbon sources and was used as a low-cost adsorbent in wastewater treatment; therefore, its use has been applied in a number of research papers. In addition, the production process of activated carbon from sawdust can serve as a viable and cost-effective alternative technique, both in terms of environmental impact and economic feasibility, where the emissions of greenhouse gases resulting from the synthesis of 1 kg of activated carbon by the utilization of sawdust were assessed. This approach decreased the global warming potential by approximately 9.69 E + 00 kg CO2-eq (M. H. Kim et al. 2018a, b). Activated carbon derived from sawdust is an innovative substance that possesses numerous environmental advantages, extending beyond its ability to collect carbon. Upcycling solid waste into activated carbon provides several environmental advantages, such as decreasing the amount of solid waste in landfills. The distinctive pore structure of the activated carbon derived from pine sawdust also enables the capture of many environmental contaminants, including pesticides, heavy metals, and dyes, in addition to CO2 (Patel et al. 2023).

Residential kitchens produce wastewater. Containing suspended compounds, oil, fats, and proteins. Sawdust used as absorbents in sink filters. The results show the oil removal efficiency ranges from 94 to 98%, and residual concentrations of other monitored parameters such as TDS, DO, and BOD were (794–236 mg/l), (2.95–3.02 mg/l), and (46–146 mg/l), respectively (Majid et al. 2022). Using sawdust as filter media with variable depths of 20 cm, 30 cm, and 40 cm, TSS reduced by 59.4, 66.6, and 77.1%, BOD decreased by 65.65, 70.9, and 73.61%, and COD decreased by 55.07, 69.9, and 76.6%, respectively (Elsakka et al. 2023). Activated carbon powder made from eucalyptus wood sawdust used as a low-cost adsorbent in dairy wastewater treatment has removal efficiencies of 94.8 and 89.2% for COD and TDS, respectively (Sivakumar et al. 2015). Carbon adsorbent made from Ayous sawdust was used as adsorption to remove nitrogen, phosphate, and carbon loads from SWW for an equilibrium time of 60 min. The reduction ratios are varying from 31 up to 52% for forms of nitrogen, as well as 40.7% and 52% for organic matter and phosphate, respectively (Djonga et al. 2021). Sawdust biochar/Fe3O4 nanocomposite is used as an adsorbent to remove textile dye Reactive Blue 21 (RB21) in textile wastewater and achieve a removal ratio up to 75% under ideal conditions (Nadeem et al. 2019).

Sand filter used as second stage for industrial wastewater treatment. The sand/gravel filter is tested to treat cheese-processing effluent with daily organic loads of 42,000 and 84,000 mg COD/m3/day, and the pH value ranges from 7.0 to 12.7. The filter achieved a removal ratio of BOD and COD of 99% and 85%, respectively (Xi et al. 2005). Bench scale models of sand filters had excellent performance in turkey processing wastewater, with over 94% TOC and 98% BOD removal (Kang et al. 2007). Multilayer sand bioreactors have been tested for dairy wastewater treatment; the removal ratio of BOD obtained by a single-layer filter was 76% and 85% for a double-layer filter, while by adding a third layer of pea gravel, the removal ratio of BOD was 79% (Liu et al. 1999). Environmental challenges have prompted the advancement of process intensification strategies designed to enhance the efficiency of current processes via innovative integrations of unit operations. In this context, membrane technology has the potential to make a significant contribution (Capizzano et al. 2022; Enrico Drioli 2018). Nonwoven textile media used to treat greywater on a lab-scale model. The system consists of a septic tank flowed by nonwoven textile filters. Removal efficiencies obtained were 79.80%, 71.60%, and 88.40% of BOD5, COD, and TSS, respectively (Spychała and Nguyen 2019). A sand filter with prior pretreatment of geotextile layers was used; these layers were found to remove 25 to 85% of the TSS and 3 to 30% of the COD (Charchalac Ochoa et al. 2015). Woven textile material is found to be more efficient compared to nonwoven materials (Eyvaz et al. 2017). Cotton fiber materials were used for filtering industrial wastewater with petroleum products, achieving a removal efficiency of 90% (Politaeva et al. 2020). Woven fiber microfiltration membrane used for treating domestic wastewater, reduced turbidity, TSS, COD, and NO3 by 76.5, 79.8, 38.5, and 41.40%, respectively (Beck et al. 2021).

This study primarily aimed to assess the efficiency of using carbonized sawdust as a natural low-cost adsorbent for slaughterhouse wastewater treatment and, secondly, determine the optimal conditions to achieve the highest efficiency.

Materials and methods

This section presents the study site, description of the pilot plant, experimental procedure, parameters monitored, and the analytical measurements.

Study site

The SWW used in this study was obtained from a private slaughterhouse located in Orabi land suited at km 28 of Cairo-Ismailia desert road, Cairo Governorate, Egypt. The samples of SWW were collected from the effluent of the slaughterhouse before discharged to local sewer networks. They were screened at first to remove suspended solids larger than 2.0 mm, then stored in 25-L polyvinyl chloride (PVC) vessels, and refrigerated at 3 °C. The experimental study was conducted in the sanitary engineering laboratory at El Shorouk Academy, Cairo, Egypt, at coordinates 30°07′08" N, 30°36′22" E. The system was operated to evaluate the system under all operating conditions.

Slaughterhouse wastewater characterization

The characteristics of raw SWW used in this study are listed in Table 3.

Table 3 Slaughterhouses wastewater characteristic in the study
Full size table

Treatment system configuration

The lab-scale treatment system consisted of: (1) mixing process and adsorption process; (2) sedimentation process to remove suspended, dissolved solids and decrease COD and BOD; and (3) final step is filtration using textile media (Fig. 1).

Fig. 1
figure 1

Slaughterhouse treatment system experimental setup

Full size image

Adsorbent production

The production process of activated carbon from sawdust is divided into three stages.

Pretreatment of sawdust

The sawdust was collected from a local sawmill, and separation was done through a sieve to a particle size range of 53–180 µm as it is used for the adsorbents studied, while the efficiency of adsorbents is controlled by the size of particles, so it is necessary for the particles to be identical (Elboughdiri et al. 2021). Before carbonization, sawdust needs a pretreatment. The sawdust washed using warm water, then rinsed with distilled water three times to remove dust and stuck materials, and then dried at 105 °C for 3 h and let it cool in desiccators. The production process of activated carbon from sawdust is divided into three stages.

Chemically activated of biochar

The sawdust samples underwent chemical activation using phosphoric acid (H3PO4) of 1.0 M. locally made from (Alnasar factory for petrochemicals) phosphoric acid (H3PO4—85%). The sawdust was mixed with phosphoric acid (H3PO4) in a 1.0 M solution for 24 h. (Djonga et al. 2019). The resulted solution was filtered. The solid samples have been washed to remove any residual inorganic compounds and surplus unreacted chemical agents, which could possibly lead to an unwanted degradation process in the future. The samples have been dried at 105 °C (mantesteequipment: DHG-9140A-148L).

Pyrolysis of sawdust

There are two types of pyrolysis processes of sawdust: slow pyrolysis and fast pyrolysis. Each process requires a specific way to implement it. As a result, biochar is produced as a major product, as shown in Table 4.

Table 4 Pyrolysis processes
Full size table

Depending on the available laboratory equipment, slow pyrolysis will be used to produce activated carbon from sawdust (ACS). After chemical activation of the sawdust, it was heated in a muffle furnace (mantesteequipment BR-12N, 1200 °C) for the maximum temperature of 600 °C with a rate 5–7 °C per min for 1 h and 30 min (Lai et al. 2013). The obtained carbonized samples were cooled in a desiccator (HAC, desiccator, non-vacuum).

Experimental study

The batch experimental study is divided into three stages: The first stage is conducted to obtain the optimum dose of activated carbon; the second stage is done to obtain the ideal operation condition and study the effect of pH value and contact time; and the third stage is applied to evaluate the whole treatment system after the MSSF was placed.

Jar test

To test the efficiency of (ACS) and investigate the optimum dose, the standard jar test using standard methods (SM) [(APHA/AWWA/WEF, 2017; Abouelenien et al. 2022) (Phipps and Bird 900 Model Jar Tester with 6 round 1000 mL mixing beakers) was used. Raw SWW was uniformly blended and divided into 5 beakers, each 500 mL. Activated carbon was added to the beakers with different dosages of 0.25, 0.50, 1, 1.5, 2, 3, and 4 g/l (Abouelenien et al. 2022; Ahmed et al. 2022). The two stages of the jar test were conducted: rapid mixing and slow mixing. Rabid mixing with 180 rpm for 3 min, slow mixing with 60 rpm for 30 min, then settling allowed to occur for 1.0 h.

Treatment procedure

After the optimum dose of ACS was obtained, the treatment system was a simplified batch system. The treatment system was done in three steps. The first step mixing stage was done in a 7-L glass vessel with variable mixing time, which expresses the contact time between the ACS and SWW (30, 40, 60, 80, 100, 120, and 140) min. (Elsakka et al. 2023) using mechanical stirring (Lachoi LCH-OES-30LFR) with 60 rpm. Then the sedimentation stage occurs for 2.0 h in the same 7-L glass vessel to find the suitable contact time for the adsorption process. Where the second stage was applied to study the effect of pH value on the adsorption process, the pH value was changed to be (2, 4, 6, 8, and 10) (Elsakka et al. 2023; Pathak et al. 2016) while keeping the contact time, ACS dose, and sedimentation time constant.

After getting the optimum contact time and optimum pH value, the resultant effluent was filtered through a slow sand filter in PVC pipe with a diameter 10 cm as a third stage of treatment and a maximum water depth of 15 cm. A woven textile cotton media was placed on the surface of the sand media, and the specifications of the layers are as follows: -

Coarse gravel media.

  • Effective size of sand = (3.0–4.0) cm

  • Depth of layer = 10 cm

Sand media:

  • Effective size of sand = (0.25–0.35) mm

  • Depth of layer = 15 cm

Woven cotton media:

A single layer of woven cotton media was used above the sand layer with the following characteristics: -

  • Fiber thickness = 27 * 27 Ne

  • Pore size = 0.0018 mm

Analytical experimental measurements

Three sampling points were chosen to evaluate system efficiency: before mixing, after sedimentation, and after a modified slow sand filter. All the samples were analyzed in the laboratories of the Higher Institute of Engineering, El Shorouk Academy, and the Central Laboratories of the Wastewater Holding Company using standard methods (SM) (APHA/AWWA/WEF, 2017). The parameters observed include pH values, total suspended solids (TSS), chemical oxygen demand (COD), biochemical oxygen demand (BOD), total nitrogen, total phosphorus, total coliform count (TCC), and fecal coliform count (FCC).

A multi-channel analyzer (Topac Consort C932) was used for pH value recoding. BOD values were measured using 300-mL incubation bottles and a Hach HRI3P-2 (220V) incubator, while COD values were measured using the closed reflux colorimetric method using a UV–VIS DR3900 laboratory and a Hach spectrophotometer with a wavelength range from 320 to 1100 nm. TN and TP values measured using a Hach BioTector B7000 TOC/TN/TP Analyzer. E. coli and FC were measured using Quanti-Tray and Quanti-Tray 2000 (SM 9223 B).

Results and discussion

Jar test results

Table 5 shows the removal efficiency for the monitored parameters using different doses of activated carbon after slow mixing for 30 min and setting for 1.0 h.

Table 5 Effect of dose difference
Full size table

From Table 5, by increasing the doses of activated carbon as an absorbent, the removal ratios for all parameters increase while the contact time remains constant for 30 min. The dose of 2.0 g/l yielded significant removal ratios of up to 51% when the dose of activated carbon was slightly increased. The increase in adsorption with an increase in ACS dosage can be attributed to a larger surface area and a greater availability of adsorption surface sites and exchangeable sites for the ions (Sharma et al. 2010).

Effect of contact time on the adsorption process

The effect of changing the contact time of the adsorption process was studied in order to obtain the ideal contact time for the adsorption process. The optimum dose used was 2.0 g/l with a constant mixing speed of 60 rpm.

The rate of adsorption increased with time when it was fast during the first 60 min, and the rate began to increase slowly until 100 min; after that, the rate increased slightly. So that the optimum time of the adsorption process was 100 min because if duration increases more than that, no noticeable progress will occur. This could be attributed to the unavailability of reactions, which decreases with time.

Figure 2 illustrates the removal efficiency of monitored parameters. The average removal rates for turbidity, TSS, and TDS were 71.34 ± 5.81, 81.93 ± 6.25, and 45.59 ± 8.45%, respectively. The highest removal ratios of BOD and COD after 100 min were 68.47 ± 6.23 and 65.37 ± 8.53%, respectively. Both of the TP and TN removal ratios were 48.85 ± 7.12 and 51.80 ± 6.89, respectively; the removal rates were acceptable but lower than the other parameters.

Fig. 2
figure 2

Removal efficiencies under the effect of contact time: a turbidity, total suspended solids (TSS), and total dissolved solids (TDS); b chemical oxygen demand (COD) and biological oxygen demand (BOD); c total phosphorus (TP) and total nitrogen (N)

Full size image
Fig. 3
figure 3

Monitored parameters removal efficiencies under the effect of pH value: a turbidity, total suspended solids (TSS), and total dissolved solids (TDS); b chemical oxygen demand (COD) and biological oxygen demand (BOD); c total phosphorus (TP) and total nitrogen (N)

Full size image

The adsorption capacity yield of the adsorption decreased after it reached the point at which it should be removed. This is attributed to the fact that the desorption process is initiated by the duration of contact times between the adsorbent and adsorbate, which is longer than the exemplary contact time (Mall et al. 2005). And it is also due to the gathering of molecules as contact time increases, which obstructs their ability to penetrate deeper into the adsorbent structure at areas with higher energy. This aggregation decreases the impact of contact time as the pores become filled and begin to impede the diffusion of aggregated molecules in the adsorbents (Wahyuhadi et al. 2023).

Effect of pH

pH value in the solution is considered the most important factor affecting the uptake of cations from aqueous solutions depicted; its effect is not only the surface charge of the biosorbent but also the ionization of the organic molecules, as well as the dissociation of functional groups on the active sites of the sorbent. In this study, the pH ranges from 2 to 10, from a highly acidic range to high alkaline, while maintaining all other parameters constant, like the adsorbent dosage of 2.0 g/l and the contact time of 100 min. In order to adjust the pH value, locally made chemicals from the Alnasar factory for petrochemicals were used. Sodium hydroxide (NaOH–99%) is used to increase the pH value, while sulfuric acid (H2SO4–98%) is used to decrease the pH value.

Figure 3 shows the removal efficiencies of the monitored parameters decreased as pH increased, where the best results were obtained. pH values range from 4 to 6. The removal ratios of turbidity, TSS, and TDS were 80.52 ± 4.23, 82.13 ± 1.56, and 48.59 ± 5.12% in the case of pH value 4, and 78.30 ± 3.52, 80.20 ± 2.33, and 47.60 ± 6.88 when pH value was 6, respectively. Furthermore, the organic removal process is more advantageous at lower pH levels because the adsorbent surface acquires a net negative charge when functional groups dissociate at higher pH and a positive charge at lower pH (Moreno-Castilla 2004). The achieved removal ratio of BOD and COD was up to 82.13 ± 3.87 and 78.84 ± 6.65%, respectively. The highest removal ratios of TP and TN were up to 65.52 ± 1.12 and 67.73 ± 3.44%, respectively. When the pH values reached 10, there was a severe deterioration in the removal ratios for all parameters.

On the other hand, the bacterial count decreased as the pH decreased, indicating that an acidic condition could lead to the elimination of fecal coliform, which requires a pH range of 5.5 to 7.5 to remain viable. The microbial content of TCC (total Coliform count) and FCC (fecal Coliform count) was 4.12E + 12 and 1.01E + 4, with removal efficiencies of 85.30 ± 3.2% and 91.34 ± 5.6%, respectively, for pH value 4.0 as extremely acidic.

Effect of textile filter

The modified slow sand filter (MSSF) was operated for 30 days after the sedimentation process with a constant flow rate of 50 L/day. While the contact time was 100 min and the pH value was stetted at 4.0 with a constant dose of 2.0 g/l. The filter was operated for 3.0 days before operation for adjustment and for the initial growth of dirty skin on the woven cotton layer. Figure 4 explicates the performance of MSSF.

Fig. 4
figure 4

Monitored parameters removal efficiencies after MSSF: a turbidity, total suspended solids (TSS), and total dissolved solids (TDS); b chemical oxygen demand (COD) and biological oxygen demand (BOD); c total phosphorus (TP) and total nitrogen (N)

Full size image

The average removal ratios of turbidity, TSS, and TDS were 97.14 ± 2.40, 98.96 ± 1.55, and 81.17 ± 5.16%, respectively. When the MSSF achieves an impressive average removal percentage of BOD and COD after 30 days of operation, up to 94.80 ± 4.22 and 91.80 ± 3.64. The removal percentages of TP and TN are acceptable but slightly lower compared with other parameters, where the average removal rates were 81.12 ± 8.15% and 82.50 ± 6.77%. The MSSF with modified woven textile cotton media improved the performance of the treatment system by a percentage range of 13.71% to 32.58% for all parameters. The bacterial counts of TCC and FCC were 3.0E + 11 and 1.10E + 03, achieving removal ratios 98.93 ± 1.10 and 99.13 ± 0.40, respectively. This is attributed to the formation of biologically dirty skin on the top of the MSSF media layer.

The results in Fig. 4 expressed the evaluation of the whole system with the ideal condition of operation, which was obtained through the experimental model, which boils down to ACS 2.0 g/l, the optimum contact time for the adsorption process 100 min, and the pH value adjusted to 4.0.

By comparing the results obtained with previous studies, it was found that Bazrafshan et al. (Bazrafshan et al. 2012) acquired COD and BOD removal ratios of 99% using chemical coagulation and electrocoagulation processes, which is higher than the obtained removal ratio in this study by 6%–8%. The COD removal ratio in the current study was higher than the removal percentage achieved by Al-Mutairi et al. (ALMUTAIRI, 2004) and Amuda and Alade (Amuda and Alade 2006). They reach 45–75% via chemical coagulation by adding aluminum salts and polymer compounds. The obtained TCOD removal ratio was higher than the removal percentage of Rajakumar et al. (Rajakumar et al. 2012) when they used a hybrid up-flow anaerobic sludge blanket reactor, achieving removal ratios ranging from 70 to 86%. In addition, COD and BOD reduction percentages fall within a similar range as those attained by Sunder and Satyanarayan (Sunder and Satyanarayan 2013), who gained removal percentages of 86.0%–93.58% and 88.9%–95.71%, respectively, via the anaerobic treatment. The system successfully removed TCC and FCC with maximum removal ratios of 99 ± 0.14% for both, which were higher than the achieved values by El-Sesy and Mahran (El-Sesy and Mahran 2020), who recorded 88%-92% by using the ethanolic extract of Psidium guajava (1.5 g) to determine the percentage of total viable bacterial counts removed from treated wastewater samples. Fatma Abouelenien et al. (Abouelenien et al. 2022) obtain removal ratios of 90.58%, 83.47%, and 88.75% of BOD, COD, and TSS using a combination of natural zeolite (1200 mg/l) and a rice straw filter, which is lower than that obtained using ASC and MSSF, while the removal rate of TCC was almost the same within limits 99.9%. Philadelphia Vutivi et al. (Ngobeni et al. 2022) used Ecoflush™ and electrocoagulation (EC) for poultry slaughterhouse wastewater treatment, where the EC produced high-quality effluent with a reduction in COD of 92.40%, which is slightly higher than the removal rate in this research, 91.80%. While when used (EcoflushTM), the COD reduction was 20%–50%, however, the combination of both processes, EcoflushTM and EC, did not have substantial disparity. These results were higher than those reported by Edris Bazrafshan et al. (Bazrafshan et al. 2022), who reported an 89.55% for COD, 88.88% for BOD, 91.27% for TSS, 69.23% for TKN, and 100% for FC. When they used a combination of chemical coagulation and electro-Fenton methods, the results in Fig. 4 show that the removal efficiency of BOD 94.80%, COD 91.80%, and TSS 98.96% is lower than that obtained by C.-K. Chen and S.-L. Lo (Chen and Lo 2003), who used the activated sludge/contact aeration process, achieving 97% for BOD and 96% for COD, while the removal rate of TSS 95% is lower than that obtained currently, in contrast with Asad Ashraf and Izharul Haq Farooqi (Ashraf and Farooqi 2022) obtaining removal percentages of BOD 84%, COD 80%, and TSS 87%, respectively, using the SBR reactor, in addition to when they operated the SBR after the DAF unit. The results got worse, achieving BOD, COD, and TSS removal percentages of 80, 81, and 73%, respectively. While the removal rates of both TKN and phosphorus have improved to 81 and 69% instead of 61% and 68%, but remain lower than what was obtained in the current study, 82.5 and 81.12%, respectively. Bohdziewicz and Sroka (Bohdziewicz and Sroka 2005) studied the performance of using RO technology as second stage after activated sludge process; this combination achieves removal efficiency 85.8 and 50% of BOD and COD, respectively, where is lower than obtained in current study which was consistent with the results obtained by Yordanov [(D. YORDANOV 2010)] who investigated the using of ultra-filtration (UF) where BOD and COD removals were 97.80–97.89% and 94.52—94.74%, respectively; however, the removal percentages of TP and TN were 97.5 and 90% which were higher than the results obtained in this study and higher than results obtained by Gürel and Büyükgüngor (Gürel and Büyükgüngör, 2011) who examined the performance of membrane bioreactors (MBRs) for nutrients removal from SWW; removals were obtained for TN, TP of 44, 65%.

Hence, we notice that using ACS followed by MSSF for slaughterhouse wastewater treatment, the results achieved are acceptable. There is no sludge or disposed materials, as the ACS can be regenerated under conditions similar to the production process (Larasati et al. 2021; Oladejo et al. 2020), and it can be reused again in the treatment process. And also, the woven cotton layer used in MSSF was washed with a water jet and returned back due the drop in flow rate as resource optimization.

Although the pilot-scale process effectively removed pollutants from SWW, the resulting does not meet the standard requirements for wastewater disposal in terms of any of the measured parameters, except for TSS, TDS, and TP. This is evident from Table 2, according to Egyptian Standard Law 48, 1982, and Decree 8, 1993. This could be due to the presence of unprocessed SWW with a high concentration of blood, as the samples were taken directly from the slaughterhouse without any dilution or pretreatment and without removing the blood. Therefore, additional research is required to enhance this procedure. There is an outdoor pilot-scale model being built and will be erected at the slaughterhouse location with additional pretreatment processes to remove blood before applying this technique, and the results will be published in a separate research paper. And also, simulations can be performed using the TOXCHEM model to control and predict the ASC dosage and removal rates of pollutants and gas emissions (Nile et al. 2024; Hamad et al. 2023).

Cost analysis

Treatment cost analysis was conducted for treated slaughterhouse wastewater (SWW), including the cost of chemical agents and electricity for optimum operation conditions; this cost does not include construction costs, as it is only a laboratory model.

  • Quantity of treated wastewater = 1.50 m.3

  • Power consumption = 5.3 Kw

  • Cost of electricity = 10.30 * 1.36 = 14.0 EGP

  • Cost of phosphoric acid = 380.0 EGP

  • Cost of sodium hydroxide = 275.0 EGP

  • Cost of sulfuric acid = 150.0 EGP

  • Cost of woven cotton media = 26 EGP

  • Cost of sand and Gravel = 10 EGP

  • Total cost = 855/1.5 = 570 EGP/m.3

Conventional slaughterhouse wastewater treatment cost (operation cost) = 2000 EGP/m.3

Cost saving = 2000 – 570 = 1430 EGP/m.3

Percentage cost savings = 1430/2000 = 71.50%

From the above rough cost calculations, we can deduce that the use of the ACS followed by MSSF reduced about 71.50% of the conventional SWW treatment methods.

Conclusion

This study used a lap-scale model to treat SWW, which involves three steps in the treatment process: mixing and adsorption using ACS, followed by sedimentation. The final step was filtration using a slow sand filter, with a modified layer of woven textile cotton on top of the SSF.

The initial step of the experimental program involved a jar test to determine the optimal dose of ACS. We separately tested the initial two steps, varying parameters like pH value and contact time while maintaining a constant ACS dose, to determine the ideal operation condition. The final step in system evaluation was to examine the MSSF.

The best results were found when the ACS dose was 2.0 g/l. These percentages were for turbidity (37.08%), BOD (37.36%), COD (35.99%), TSS (38.30%), TDS (34.48%), TP (26.83%), and TN (34.48%). Increasing the contact time to 100 min improved the results, yielding removal percentages of 71.34, 81.93, and 45.85% for turbidity, TSS, and TDS, along with 68.47 and 65.37% for BOD and COD. Furthermore, TP and TN removal rates improved, reaching 48.85 and 51.80%, respectively.

As the pH value fluctuated while the contact time stayed constant at 100 min, the results fluctuated as well. The pH value that yielded the best results was 4.0, with the removal ratios of the monitored parameters being 80.52, 85.25, and 48.59% for turbidity, TSS, and TDS, and 82.13 and 78.84% for BOD and COD. Also, TP and TN removal rates improved, reaching 65.52 and 67.73%, respectively.

We achieved the best removal efficiencies at 97.14%, 94.80%, 91.80, 98.96, 81.17%, 81.12, and 82.50% for turbidity, BOD, COD, TSS, TDS, TP, and TN, respectively, after implementing a modified slow sand filter (MSSF) and assessing the pilot test system as a whole. This is in addition to the filter's ability to remove bacteria count at a rate of up to 98.93 and 99.13% of TCC and FCC.