The designed combined poultry slaughterhouse wastewater treatment system involving sedimentation, EC process, ultrafiltration, and UV treatment will show exceptional results as removal efficiencies for almost all indicators are within the quality standards. Also, the wastewater after treatment will be 100% free from microbe colonies. The technology is proposed for obtaining technical water from the wastewater with antioxidant properties for washing and disinfecting equipment and premises of poultry farms, not affecting the quality of poultry products (important for food safety standards (Nagyová et al., 2019)). The project will reduce the volume of water consumption of the poultry industry, which is one of the important indicators of "green technology".

Table 1 below shows the characteristic of wastewater obtained from Izhevskoe a Kazakhstani company. The sample is from cooling section and was kept at 4 ℃ once delivered to the lab. To examine characteristics of the wastewater, analytical methods were used which are described in the following section. Also, before conducting the experiment, calcium chloride was added to the wastewater for the EC process.

In this study, a combined system is used which comprises of EC process, ultrafiltration, and photochemical purification. Figure depicts the schematic of the lab combined system used. First, the mini reservoir collects the wastewater and filters large particles such as feathers or organic components, using the macro-filter added. The effluent then leaves the reservoir and enter the electrolyte cell in which the EC process occurs for about 30 min. This electrolyte cell is made from polypropylene material with the dimensions 15 x 13 x 11 cm. The electrodes plate dimension used were 10.5 x 11.5 x 0.2 cm and 10.5 x 10.5 x 0.8 cm for aluminium (anode) and graphite (cathode) electrodes respectively. These electrodes were connected to direct current supply (Xinhua electrical weld company, China) characterized by the ranges 0 – 10 A for operating current and 0 – 12 V for voltage. Usually, electrodes selected are iron and aluminium as they are cheap and readily available. However, in our previous study, we have mentioned that using graphite is a better option as it is inert and does not consumes, making it not only efficient but also cost-effective (Meiramkulova et al., 2018d).

Once EC is completed, processed water is then transferred to the sedimentary cylinder where any organic matter is collected. A pump with a pressure of up to 5.5 bar, allows the water to flow from the sedimentary cylinder to the ultrafilter. This ultrafilter has a pore size of 0.02 μm, sufficient to trap most sediments, bacteria, and viruses. Finally, the ultra-filtered water flows to a small reservoir where a small pump is used to recirculate the water through an UV sterilizer for 10 min to kill any remaining microorganism in the water. Overall, this process lasted for about 40 min.

Calcium chloride was added as an electrolyte to all samples before electrolysis, which decreases pH level of the wastewater and prevent basic condition from occurring which can lead to formation of ammonia gas that can be harmful to the environment. Furthermore, the formation of hypochlorite ions occurs during the EC process. Then, at anode molecular chlorine consequently hydrolyses in neutral water condition, hence, reducing its concentration (Czarnetzki and Janssen, 1992).

2 C l − − 2 e − → C l 2 C l 2 + H 2 O → H C l O + H + + C l −

Phosphorus compounds present in the PSW are represented as polyphosphates, orthophosphates, and organic phosphorus-containing compounds. They can be present in the form of dissolved, colloidal and suspended state as phosphate ions. During EC treatment, phosphate ions released combine with a metal ion to produce metal phosphates, reducing the total phosphate presence in the treated water (Emerson and Widmer, 1978).

As for nitrogen containing compounds, urea is a main by-product of the organisms. It can be found in animal-based industrial wastewater as ammonium carbonate under the impact of putrefying bacteria (Barmaki et al., 2009).

C O ( N H 2 ) 2 + 2 H 2 O → ( N H 4 ) 2 C O 3

However, it degrades and results in carbon dioxide and ammonia.

( N H 4 ) 2 C O 3 → 2 N H 3 + C O 2 + H 2 O

Ammonia then transforms into nitrite and nitrate ions by consuming oxygen under the impact of nitrifying bacteria as it is shown below (Pan et al., 2018).

Nitrification:

1-step  N H 4 + + 2 O 2 → N O 2 − + H 2 O + H + 2-step  N O 2 − + 0.5 O 2 → N O 3 − + H 2 O + H +

Then nitrate ions combine with metal ions. Thereby, nitrates are neutralized, again reducing its concentration in the treated water.

Furthermore, ammonia reacts with hypochlorite ions and produces monochloramine and dichloramine in acidic condition (Asano et al., 2005). Later, mono and dichloramines results in nitrogen gas.

N H 3 + H C l O → N H 2 C l + H 2 O N H 2 C l + H C l O → N H C l 2 + H 2 O N H 2 C l + N H C l 2 → N 2 + 3 H C l

All these reactions allow the reduction of pollutants in the wastewater.

The data obtained for the pollutant level in the poultry slaughterhouse wastewater was measured locally within the university lab. The following equipment was used in the measurements of the pollutant concentration: Standard Operating Procedure for GLNPO Turbidity: Nephelometric Method and American Public Health Association 4500-Nor, were used to determine the turbidity of the samples, and total bound nitrogen (TN) and total phosphorus (TP) respectively. Spectrophotometer (Hach DR3900, HACH / LANGE, Germany), standard reagents and test kits were used for the reliability of the chemical analysis. Furthermore, lab pH-meter (Hach Co), was used to measure pH values.

In accordance with the regulatory requirements of industrial and drinking water of the Republic of Kazakhstan, sanitary and microbiological examination of water before and after treatment was done based on 3 indicators:

Total microbial count (TBC) is an indicator for assessing total bacterial contamination.

The calculation was performed through:

x = a * 100 V

x - number of colonies per 100 mL;

For the processing of the microbiological data of water before and after combined cleaning from defeathering, evisceration, cooling sections a statistical analysis Wilcoxon T-test was carried out (n = 8). This study suggested a hypothesis H₀: indicators after the experiment is less than the values of the indicators before the experiment; H1 indicators after the treatment more than the values before the experiment.

The critical values for the Wilcoxon T-test for n = 8:

T_cr=1(p ≤0.01)

In this case, the empirical value of T falls into the zone of significance: T_emp < T_cr.

Hypothesis H₀ is accepted for all sections.