Abstract
The growing sector of dairy industry in Bulgaria leads to large waste stream formation with high pollution variation, which require specific treatment application. In the present research different fractions and wash waters from the production of kashkaval and white brined cheese, milk curd, strained yoghurt manufactured in three medium-type Bulgarian milk processing plants were studied. The basic indicators for wastewater quality: total solids (TS), total suspended solids (TSS), active reaction, fat, oil and grease (FOG), 5-day biological oxygen demand (BOD5), chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) were analysed by standard procedures. The obtained results indicate that kashkaval whey from the sheep’s milk processing was the most contaminated effluent, reaching COD more than 68,000 mg O2/dm3 and BOD5 - up to 37,000 mg O2/dm3. Such high concentrated wastewaters can be treated only by anaerobic methods. Secondary cheese whey (SCW) has less impurities than cheese whey, but its soluble milk fractions are difficult to biodegrade, resulting in BOD5:COD ratio lower than 0.40. Application of membrane technologies in milk co-product processing remove totally FOG from the SCW, where BOD5 and COD values are around 950 and 2.500 mg O2/dm3, respectively. However, the TN concentration in it is not enough to apply directly aerobic utilization. This method is the most appropriate for washing waters, which occupy both the largest volume and the cleanest fractions of all milk effluents. Future combinations of different dairy wastewaters will show the best utilization protocol for each of the milk processing plant.
Keywords:
industrial dairy wastewater composition; whey; second cheese whey; washing water
HIGHLIGHTS
Whey and wash waters from three dairy multiproduct plants are studied.
Effluents are compared by TS, TSS, active reaction, FOG, BOD, COD, TN and TP values.
Kashkaval whey from sheep's milk processing is the most contaminated fraction.
Wash waters are cleanest dairy effluents but have largest volumetric load.
INTRODUCTION
The dairy industry has deep traditions in Bulgaria [11 Aleksandrova L, Mihailov V. National Dairy Association: There is enough Bulgarian raw material. [Internet] 2020 [cited: 2023 March 12]. Available from: https://agrozona.bg/vladislav-mihaylov-natsionalnata-asotsiatsiya-na-mlekoprerabotvatelite-balgarska-surovina/. (In Bulgarian)
https://agrozona.bg/vladislav-mihaylov-n...
]. In recent years, a positive trend in the consumption of dairy foods has been observed in the domestic market [22 Status and trends of the production of milk and milk products in Bulgaria. Ministry of Agriculture and Food. Directorate of Market Measures and Producer Organizations. [Internet] 2018 [cited: 2023 Feb 22]; Available from: https://www.mzh.government.bg/media/filer_public/2018/03/01/mliako.pdf. (In Bulgarian)
https://www.mzh.government.bg/media/file...
,33 Sectoral analysis in the milk processing sector. Current trends, issues and needs. Project BG051PO001-2.1.06. Development and implementation of an information system for assessing the competencies of the workforce by branches and regions. Bulgarian Industrial Association. Sofia, Bulgaria. [Internet] 2013 [cited: 2023 May 25]; Available from: https://www.bia-bg.com/uploads/files/analysis/ISOK/533_16-Mlekoprerabotvane-2013_signed.pdf. (In Bulgarian)
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]. The production of white brined cheese, kashkaval and Bulgarian yogurt is the most represented, but the variety of products offered is increasing [44 Milk products. Plovdiv, Bulgaria: Dimitar Madjarov. [Internet] 2023 [cited: 2023 March 28]; Available from: https://madjarov.bg/product-category/mlechni-produkti/. (In Bulgarian)
https://madjarov.bg/product-category/mle...
5 Products. Sofia, Bulgaria: Milky Group Bio Private Limited Company. [Internet] 2023 [cited: 2023 March 24]; Available from: https://sayana.bg/. (In Bulgarian)
https://sayana.bg...
6 Products. Domlyan, Karlovo, Bulgaria: Polyday-2. [Internet] 2023 [cited: 2023 March 29]; Available from: https://domlian.com/products/. (In Bulgarian)
https://domlian.com/products...
7 Our products. Ovcharovo, Dobrich, Bulgaria: Dobruja Dairy Company. [Internet] 2023 [cited: 2023 March 29]; Available from: https://dobrotitsa.bg/produkti/. (In Bulgarian)
https://dobrotitsa.bg/produkti...
8 Products. Sofia, Bulgaria: Milk products. Zorov 91. [Internet] 2023 [cited: 2023 March 29]; Available from: https://parshevitsa.com/produkti/. (In Bulgarian)
https://parshevitsa.com/produkti...
-99 Products. Plovdiv, Bulgaria. United Milk Company Private Limited Company [Internet] 2023 [cited: 2023 March 29]; Available from: https://vereia.bg/groups/. (In Bulgarian)
https://vereia.bg/groups...
].
Moreover, this sector is one of the main consumers of drinking water in the food industry [1010 Prashanthi M, Sundaram R. Integrated waste management in India. Environmental science and engineering. Cham: Springer; 2016. Part V, Impact of waste on human health and community participation in waste management. Impact of dairy effluent on environment - a review; p. 239-249.,1111 Stasinakis AS, Charalambous P, Vyrides. Dairy wastewater management in EU: produced amounts, existing legislation, applied treatment processes and future challenges. J Envir Manag 2022;303:114152.]. The large assortment and applied technologies lead to the production of waste streams of different quantity and quality [1212 Rivas J, Prazeres AR, Carvalho F. Aerobic biodegradation of precoagulated cheese whey wastewater. J Agric Food Chem 2011;59:2511-7.,1313 Salas-Vargas C, Brunett-Pérez L, Espinosa-Ortiz VE, Martínez-García CG. Environmental impact of Oaxaca cheese production and wastewater from artisanal dairies under two scenarios in Aculco, State of Mexico. J Clean Prod 2021;311:127586.]. A good knowledge of the composition and characteristics of waters creates a prerequisite for their correct treatment [1414 Elliot S. Reference module in earth systems and environmental sciences. London: Elsevier; 2015. Wastewater treatment & water reclamation; p. 2-4.]. The most polluted are the waste streams from the production of white brined cheese, kashkaval, cottage cheese, condensed milk and others, which are often thrown away without further treatment [1515 Kaur N. Different treatment techniques of dairy wastewater. Gr Sust Dev 2021;14:100640.]. No less significant are the washing waters obtained from the cleaning of the technological equipment [1616 Meneses YE, Flores RA. Feasibility, safety, and economic implications of whey-recovered water in cleaning-in-place systems: a case study on water conservation for the dairy industry. J Dairy Sci 2016;99(5):3396-407.]. The main pollutants in them are organic compounds such as lactose, water-soluble proteins, emulsified lipids, mineral substances and detergents, which are the cause of high values of BOD, COD, insoluble solids, nitrogen compounds [1717 Farizoglu B, Keskinler B, Yildiz E, Nuhoglu A. Simultaneous removal of C, N, P from cheese whey by jet loop membrane bioreactor (JLMBR). J Hazard Mater 2007;146:399-407.
18 Sar T, Harirchi S, Ramezani M, Bulkan G, Akbas M, Pandey A, et al. Potential utilization of dairy industries by-products and wastes through microbial processes: a critical review. Sci Tot Envir 2021;810:152253.
19 Zandona E, Blažić M, Jambrak AR. Whey utilization: sustainable uses and environmental approach. Food Technol Biotechnol 2021;59(2):147-61.-2020 Stancheva M, Yemendzhiev H, Nenov V. Phosphorus recovery from dairy processing waste streams. J Chem Technol Metall 2022;57(1):119-125.]. The rapid decay of the large amount of organic matter can create problems when processing these wastewaters in urban treatment plants, and their direct discharge into surface water bodies is highly undesirable [2121 Vasina AI, Basamykina AN. Local wastewater treatment plant for dairy production: challenges and solutions. In: 2022 IOP Conference Series: Earth and Environmental Science. 2022;988:032077.,2222 Struk-Sokolowska J, Rodziewicz J, Mielcarek A. Effect of dairy wastewater on changes in COD fractions in technical-scale SBR type reactors. Wat Sci Technol 2017;1:156-69.]. Therefore, it is necessary to look for opportunities for their purification before release into the environment. The presence of different components in the wastewater of the dairy industry requires the application of a multi-level treatment approach [2323 Ghatawat P, Vankar Y, Dhume S, Chendake Y. Separation and recovery of milk components from dairy effluent. Int J Eng Res Technol 2019;8(6):884-8.]. Despite studies in the field, published data on the composition of industrial wastewater from dairy plants are few [2424 Moo-Young, M, Anderson, WA, Chakrabarty, AM. Environmental biotechnology. Dordrecht: Springer; 1995. Full scale anaerobic treatment of dairy wastewater using the SNC multiplate reactor; p. 544-5.
25 Ekka B, Mierina I, Juhna T, Turks M, Kokina K. Quantification of different fatty acids in raw dairy wastewater. Cleaner Eng Technol 2020;7:100430.
26 Demirel B, Yenigun O, Onay TT. Anaerobic treatment of dairy wastewaters: a review. Process Biochem 2005;40:2583-95.
27 Wang, LK, Hung, YT, Lo, HH, Yapijakis, C. Waste treatment in the food processing industry. Boca Raton: CRC Press; 2006. Chapter 1, Treatment of dairy processing wastewaters; p.1-25.-2828 Joshiba GJ, Kumar PS, Femina CC, Jayashree E, Racchana R, Sivamesan S. Critical review on biological treatment strategies of dairy wastewater. Desal Wat Treat 2019;160:94-109.], and for Bulgaria - the information is insufficient [2929 Nikolova M, Panayotov P, Taneva D. Characteristics of wastewaters from the production of yellow and white brined cheese in Bulgaria and possibilities for their treatment. In:2019 Youth Forum. Science, Technologies, Innovations and Business; 2019 May 30 - 31, Plovdiv: Non-Profit Association, Territorial Organization of Scientific and Technical Union with Home of Science and Technology, Plovdiv. (In Bulgarian)].
The purpose of the present study is to characterize the waste streams from the production of white brine cheese, kashkaval, milk curd, yoghurt and strained yoghurt from various plants in Bulgaria.
MATERIAL AND METHODS
Material
Whey and washing waters from three medium-type milk processing plants (production capacity less than 100 m3 raw milk/day) located in the region of Southern Bulgaria were studied. The first two enterprises manufacture 12 months of cow's milk and 5 months of the year sheep's milk into kashkaval, white brined cheese and whey curd obtained by filtering through cloth - for Plant 1 (P1) and through membrane processes - for Plant 2 (P2). The third factory (P3) specializes in the production of yoghurt, strained yoghurt and milk curd.
Data from the flow meters for the volume of the milk processed and waste effluents was kindly provided to us by the respective dairy plant operators.
Sampling was carried out in accordance with current legislation [3030 International Organization for Standardization. ISO 5667-10:2020. Water quality - sampling - Part 10 - Guidance on sampling of wastewater. Geneva: ISO; 2020.]. The number of annual measurements is 4 - for P1; 2 - for P2 and 4 - for P3. During the analyses, an average sample obtained from pre-homogenized, consecutively obtained 4 single samples taken at an interval of 2 h was used.
Methods
The determination of the individual parameters of the wastewaters was carried out according to the specified standards: total solids (TS) and total suspended solids (TSS) - BSS 17.1.4.04:1980 [3131 Bulgarian institute for standardization. BDS 17.1.4.04:1980. Nature protection. Hydrosphere. Water quality indicators. Method for determining the content of total solids, undissolved and dissolved substances. Sofia: BDS; 1980. (In Bulgarian)], active reaction - BSS 17.1.4.27:1980 [3232 Bulgarian institute for standardization. BDS 17.1.4.27:1980. Nature protection. Hydrosphere. Water quality indicators. Method for determining pH. Sofia, Bulgaria: BDS; 1980. (In Bulgarian).], fat, oil and grease (FOG) - EPA 1664 [3333 Environmental protection agency. Method 1664. N-hexane extractable material. Washington: EPA; 2010.], 5-day biological oxygen demand (BOD5) - ISO 1899-2:2004 [3434 International Organization for Standardization. ISO 1899:2004. Water quality - Determination of biochemical oxygen demand after n days (BODn). Geneva: ISO; 2004.], chemical oxygen demand (COD) - ISO 6060:2020 [3535 International Organization for Standardization. ISO 6060:2020. Water quality - Determination of the chemical oxygen demand. Geneva: ISO; 2020.]. The following chemical indicators were analyzed photometrically by tests from the Spectroquant® series, Merck Millipore, USA: total nitrogen (TN) - EN ISO 11905-1 [3636 International Organization for Standardization. ISO 11905-1:2001. Water quality - Determination of nitrogen - Part 1: Method using oxidative digestion with peroxodisulfate. Geneva: ISO; 2001.] and DIN 38405-9 [3737 Deutsches Institut fur Normung. DIN 38405-9. German standard methods for examination of water, waste water and sludge - Anions (group D) - Part 9: Spectrometric determination of nitrate. Berlin: DIN; 2011.], total phosphorus as orthophosphate (TP) - EN ISO 6878:2005 [3838 International Organization for Standardization. ISO 6878:2004. Water quality - Determination of phosphorus - Ammonium molybdate spectrometric method. Geneva: ISO; 2004.].
Statistical processing of the data
All wastewater analyzes were performed in triplicate. The results obtained were summarized by determining the mean value and standard deviation (± SD). Data processing was performed using the MS Office Excel 2010 software product.
RESULTS AND DISCUSSION
Whey from the production of kashkaval and white brined cheese
Regardless of the type of end product, cheese production can be summarized in the following basic steps [3939 Shivarov, M. Dairy technology: Sofia: Zemizdat; 1993. General technological scheme for the production of cheese; p. 15-216. (In Bulgarian)]. After removal of mechanical impurities and standardization in terms of casein and fat content, the milk is pasteurized and sent for biological ripening in stainless steel vessels. Subsequently, it is sent for curdling under the influence of a milk coagulating enzyme. After the required technological time, the resulting coagulum is formed, pressed, salted and matured, packaged and turned into a commercial product [4040 Walstra P, Wouters JTM, Geurts. Dairy science and technology, 2nd ed. Taylor & Francis Group; 2006. Principles of cheese making; p. 577-581.,4141 Wang LK, Tay JH, Tay STL, Hung YT. Handbook of environmental engineering, vol. 11. Environmental bioengineering. New York: Humana Press, Springer; 2010. Anaerobic treatment of milk processing wastewater; p. 555-618.]. The waste liquid component is referred to as whey [4242 Dos Reis Coimbra JS, Teixeira JA. Engineering aspects of milk and dairy products. CRC Press, Taylor & Francis group; 2010. Applications of membrane technologies in the dairy industry; p. 33-34.].
In Table 1 the results of the study of whey formed during the production of Bulgarian white brined cheese and kashkaval from cow’s and sheep’s milk in P1 and P2 are presented. The obtained data is compared with the permissible standards for discharging industrial wastewater from the dairy industry into surface runoff water bodies [4343 Regulation 6 on emission norms for the permissible content of harmful and dangerous substances in waste water discharged into water bodies 2000 (Bul). [Internet] 2000 [cited: 2022 December 17]; Available from: https://eea.government.bg/bg/legislation/water/nared6.pdf. (In Bulgarian)
https://eea.government.bg/bg/legislation...
].
The amount of separated whey in the different plants is similar - 75-90% from the volume of incoming milk, with average levels for cheese production 85-90% [4444 Scott R, Robinson RK, Wilbey RA. Cheesemaking practice. Boston: Springer; 1998. Chapter 18, Cheese whey and its uses; p. 320-1.
45 El-Tanboly E, EL-Hofi M. Recovery of cheese whey, a by-product from dairy industry for use as an animal feed. J Nutr Health Food Eng 2017;6(5):148-54.-4646 Grumezescu AM, Holvan AM. Milk-based beverages. Woodhead publishing; 2019. Chapter 14, Dairy and nondairy-based beverages as a vehicle for probiotics, prebiotics, and symbiotics: alternatives to health versus disease binomial approach through food; p. 473-520.]. More whey is formed in the production of kashkaval than that of white brined cheese. The values are 11% higher when the raw material for kashkaval is sheep's milk and 3-10% higher - from cow's milk.
TS in the whey exceed 50 g/L [4747 Pires AF, Marnotes NG, Rubio OD, Garcia AC, Pereira CD. Dairy by-products: a review on the valorization of whey and second cheese whey. Foods 2021;10(1067):1-24.], while TSS show wide variations for individual products, with the largest difference in the production of cow's milk cheese. Their content relative to TS is higher in sheep milk streams - 45% more for cheese whey in P1 and 14% - than the same in P2. Whey from P2 is richer in water-insoluble compounds in comparison with that of P1. In all cases, the TSS exceed the permissible values for discharge into water bodies by more than 99%.
Active reaction is important for the proper operation of water treatment processes [4848 Bazin MJ, Prosser JI. Physiological models in microbiology. vol. 1., 1st ed. Boca Raton: CRC Press; 1988. Chapter 6, Role of pH in biological wastewater treatment processes; p. 76-86.,4949 Luo J, Ding LH. Influence of pH on treatment of dairy wastewater by nanofiltration using shear-enhanced filtration system. Desalination 2011;278(1-3):150-6.]. The data report a typical slightly acidic environment [5050 Kumar N. The four fs for whey utilization. Bev Food World 2016;43(1):28-31.] that prevails in whey from kashkaval production compared to that from white brined cheese. It is the lowest for cheese from cow's milk in P1: 5.28 pH units. According to Regulation 6, the specified indicator is in the standards only for whey from white brined cheese from sheep's milk. The low pH value and the high content of water-soluble components, such as lactose, can result in rapid spoilage of whey, which adversely affects its subsequent biological treatment [4141 Wang LK, Tay JH, Tay STL, Hung YT. Handbook of environmental engineering, vol. 11. Environmental bioengineering. New York: Humana Press, Springer; 2010. Anaerobic treatment of milk processing wastewater; p. 555-618.,4545 El-Tanboly E, EL-Hofi M. Recovery of cheese whey, a by-product from dairy industry for use as an animal feed. J Nutr Health Food Eng 2017;6(5):148-54.,5151 Prazeres AR, Carvalho F, Rivas J. Cheese whey management: a review. J Envir Man 2012;110:48-68.].
In dairy wastewater, compounds with lipid nature are undesirable in concentrations above 10 mg/L [4343 Regulation 6 on emission norms for the permissible content of harmful and dangerous substances in waste water discharged into water bodies 2000 (Bul). [Internet] 2000 [cited: 2022 December 17]; Available from: https://eea.government.bg/bg/legislation/water/nared6.pdf. (In Bulgarian)
https://eea.government.bg/bg/legislation...
]. Larger values pose risks of clogging the pipes in the sewage system or disrupting the aerobic environment during degradation of the different dairy pollutants [5252 Sello M. Wastewater fats, oils and grease characterization, removal and uses. A review. Env Sci Ind J 2021;17(10):200.,5353 He X, Iasmin M, Dean LO, Lappi SE, Ducoste JJ, de los Reyes FL. Evidence for fat, oil and grease (FOG) deposit formation mechanisms in sewer lines. Envir Sci Technol 2011;45(10):4385-91.]. The FOG content is higher in the whey from the kashkaval production and in raw sheep's milk (Table 1). The probable reason can be the fatter sheep's milk compared to cow's [5454 Mollica MP, Trinchese G, Cimmino F, Penna E, Cavaliere G, Tudisco R, et al. Milk fatty acid profiles in different animal species: focus on the potential effect of selected PUFAs on metabolism and brain functions. Nutrients 2021;13(4):1111.]. Fats predominated in the whey of P2 - an average of 501 mg/L, or 30 mg/L more than P2. It was highest in the waste streams of sheep's kashkaval - 750 mg/L, and lowest - for white brined cheese from cow's milk - 310 mg/L, respectively 75 and 31 times above the permitted values [4343 Regulation 6 on emission norms for the permissible content of harmful and dangerous substances in waste water discharged into water bodies 2000 (Bul). [Internet] 2000 [cited: 2022 December 17]; Available from: https://eea.government.bg/bg/legislation/water/nared6.pdf. (In Bulgarian)
https://eea.government.bg/bg/legislation...
].
The choice of wastewater treatment methods directly depends on BOD5 and COD concentrations [5555 Dhall P, Siddiqui TO, Ahmad A, Kumar R, Kumar A. Restructuring BOD:COD ratio of dairy milk industrial wastewaters in BOD analysis by formulating a specific microbial seed. The Sci World J 2012;105712:1-7.,5656 Abdalla KZ, Hammam G. Correlation between biochemical oxygen demand and chemical oxygen demand for various wastewater treatment plants in Egypt to obtain the biodegradability indices. Int J Sci: Basic Appl Res 2014;13(1):42-48.]. The prevailing limit for wastewater from food processing plants under BOD5 is 50 mg/L, while for COD it is 250 mg/L [4343 Regulation 6 on emission norms for the permissible content of harmful and dangerous substances in waste water discharged into water bodies 2000 (Bul). [Internet] 2000 [cited: 2022 December 17]; Available from: https://eea.government.bg/bg/legislation/water/nared6.pdf. (In Bulgarian)
https://eea.government.bg/bg/legislation...
]. Among all waste streams from the dairy industry, cheese whey is the most loaded by these indicators [4646 Grumezescu AM, Holvan AM. Milk-based beverages. Woodhead publishing; 2019. Chapter 14, Dairy and nondairy-based beverages as a vehicle for probiotics, prebiotics, and symbiotics: alternatives to health versus disease binomial approach through food; p. 473-520.,4747 Pires AF, Marnotes NG, Rubio OD, Garcia AC, Pereira CD. Dairy by-products: a review on the valorization of whey and second cheese whey. Foods 2021;10(1067):1-24.], with values of BOD5 - 19,000-35,010 mg/L and COD - 54,100-68,300 mg/L which is 99% more than Bulgarian laws allow. Whey from sheep's milk is more contaminated than the same from cow's milk - on average 3.7 times more by BOD5 for P1 and 2.7 times more by COD for P2. The high concentration of these pollutants in whey attracts the attention to use anaerobic methods for their utilization [5757 Nyaki A, Njau K. Assessment of dairy wastewater treatment and its potential for biogas production at Tanga Fresh Limited. Tanz J Sci 2016;45(1):120-33.
58 Wang LK, Hung YT, Lo HH, Yapijakis C. Handbook of industrial and hazardous wastes treatment. 2nd ed. CRC Press; 2004. Chapter 13, Treatment of dairy processing wastewaters; p. 619-643.-5959 Strydom JP, Mostert JF, Britz TJ. Anaerobic digestion of dairy factory effluents. Water Research Report ? 455. [Internet] 2001 [cited: 2023 May 25]; Available from: https://www.wrc.org.za/wp-content/uploads/mdocs/455-1-01.pdf.
https://www.wrc.org.za/wp-content/upload...
].
The BOD5:COD ratio is important for proper determination the level of biodegradability and the technological features of wastewater treatment [6060 Andrio D, Asmura J, Yenie E, Putri K. Enhancing BOD5/COD ratio co-substrate tofu wastewater and cow dung during ozone pretreatment. In: MATEC Web of Conferences 2019. International Conference on Advances in Civil and Environmental Engineering, 2018 Oct 24 - 25; Bali. 276(06027):1-6.]. If it is above 0.5-0.6, the water can be purified biologically [6161 Dinçer AR. Increasing BOD5/COD ratio of non-biodegradable compound (reactive black 5) with ozone and catalase enzyme combination. SN Appl Sci 2020;2:736.]. For P1, only kashkaval whey from sheep’s milk (KSM 1) met the above requirements with a value of 0.51, but for P2 it was achieved both at kashkaval whey from sheep’s milk (KSM 2) - 0.54 and yellow cheese whey from cow’s milk (KCM 2) - 0.61. The results for the other types of whey exceed 0.3. This indicates that they must be purified physico-chemically before they can undergo biological treatment methods [6262 Leena AV, Meiaraj DC, Balasundaram DN. BOD/COD a measure of dairy waste treatment efficiency - a case study. IOSR J Mech Civ Eng 2016;13(5):107-14.].
Wastewater TN and TP are related to eutrophication processes in water basins [2020 Stancheva M, Yemendzhiev H, Nenov V. Phosphorus recovery from dairy processing waste streams. J Chem Technol Metall 2022;57(1):119-125.,6363 Numviyimana C, Warchol J, Izydorczyk G, Basladynska S, Chojnacka K. Struvite production from dairy processing wastewater: Optimizing reaction conditions and effects of foreign ions through multi-response experimental models. J Taiwan Inst Chem Eng 2020;117:182-9.]. All samples analyzed show that these biogenic elements exceed many times the emission norms [4343 Regulation 6 on emission norms for the permissible content of harmful and dangerous substances in waste water discharged into water bodies 2000 (Bul). [Internet] 2000 [cited: 2022 December 17]; Available from: https://eea.government.bg/bg/legislation/water/nared6.pdf. (In Bulgarian)
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]. Greater concentrations of TN were found in raw sheep's milk, in the production of kashkaval and in P2. The indicated conclusions do not apply to TP. The least polluted in terms of TN and TP is white brined cheese whey from cow’s milk manufactured in P1 (WBCCM 1), with 180 mg/L and 37 mg/L, respectively. The maximum load for TN is KSM 2 - 5,320 mg/L, while for TP is KCM 1 - 620 mg/L.
The COD:N ratio is critical for proper operation of anaerobic systems. 40:1 is considered as optimal value, although other authors share the successful operation of reactors at 80-160:1 [6464 Frigon JC, Bruneau T, Moletta R, Guiot SR. Coupled anaerobic-aerobic treatment of whey wastewater in a sequencing batch reactor: proof of concept. Water Sci Technol 2007;55(10):201-8.,6565 Zappi M, Fortela DL, Sharp W, Bajpai R, Gang D, Holmes W, et al. Evaluation of the methane production potential of catfish processing wastewater using various anaerobic digestion strategies. Processes 2019;7(368):1-15.]. Only three of the tested whey samples approach the optimal characteristics - KSM 1 - 41:1, white brined cheese whey from sheep’s milk manufactured in P1 (WBCSM 1) - 53:1 and KCM 1 - 131:1. Carbon compounds predominate in KCM 1. Whey from P2 has high concentrations of nitrogenous compounds - COD:N varies 13-22:1, which can create conditions for NH3 formation and poses a risk of inhibiting biogas fermentation [6666 Fricke K, Santen H, Wallmann R, Hüttner A, Dichtl N. Operating problems in anaerobic digestion plants resulting from nitrogen in MSW. Waste Man 2007;27:30-43.].
In well-functioning anaerobic plants, COD:P is 80-200:1 [6565 Zappi M, Fortela DL, Sharp W, Bajpai R, Gang D, Holmes W, et al. Evaluation of the methane production potential of catfish processing wastewater using various anaerobic digestion strategies. Processes 2019;7(368):1-15.]. Only WBCCM 1 is outside the specified limits with a value of 1487:1.
Secondary whey from the production of kashkaval and white brined cheese
Whey is a secondary product in the kashkaval and white brined cheese manufacturing [6767 Baltadjieva M, Slavchev G. Book for white brined cheese. Plovdiv: Academic Publishing House of UFT; 2003. Types of brined cheese - general characteristics. p. 5-68.]. It is often used as a raw material for obtaining other dairy products [6868 Mehra R, Kumar H, Kumar N, Ranvir S, Jana A, Buttar HS, et al. Whey proteins processing and emergent derivatives: an insight perspective from constituents, bioactivities, functionalities to therapeutic applications. J Func Foods 2021;87(104760):1-17.]. The fat is separated from the whey, while residual proteins are filtered through a cloth or membrane resulting whey curd [4747 Pires AF, Marnotes NG, Rubio OD, Garcia AC, Pereira CD. Dairy by-products: a review on the valorization of whey and second cheese whey. Foods 2021;10(1067):1-24.,6969 Robinson, RK. Modern dairy technology, vol. 2. Advances in milk products, 2nd ed. Blackie academic & professional, an imprint of Chapman & Hall; 2003. Chapter 2, Modern cheesemaking: hard cheeses. p. 49-217.]. The waste permeate forms the so-called second cheese whey (SCW) [7070 Rollini M, Musatti A, Cavicchioli D, Bussini D, Farris D, Farris S, et al. From cheese whey permeate to sakacin-A/bacterial cellulose nanocrystal conjugates for antimicrobial food packaging applications: a circular economy case study. Sci Rep 2020;10:21358.]. Although the last is most commonly disposed of in waste streams, it is less studied than whey [4747 Pires AF, Marnotes NG, Rubio OD, Garcia AC, Pereira CD. Dairy by-products: a review on the valorization of whey and second cheese whey. Foods 2021;10(1067):1-24.,7171 Tatoulis T, Tekerlekopouloi A, Akratos C, Pavlou S, Vayenas D. Aerobic biological treatment of second cheese whey in suspended and attached growth reactors. J Chem Technol Biotechnol 2015;90(11):2040-9.].
In Table 2 the results of the characterization of SCW obtained during the production of cottage cheese by filtration through cloth in P1 and through a membrane in P2 are summarized. The volume of SCW is similar in the different industries - on average about 0.91 m3/m3 of milk.
Tatoulis, 2014 summarized that the TS concentration in the SCW did not differ from that in the whey [7171 Tatoulis T, Tekerlekopouloi A, Akratos C, Pavlou S, Vayenas D. Aerobic biological treatment of second cheese whey in suspended and attached growth reactors. J Chem Technol Biotechnol 2015;90(11):2040-9.]. Our results support the mentioned statement. However, the data from Table 2 shows a decrease in this indicator, which for P1 is in the range of 5-23.5%. The probable reason for the wide range of the TS reduction is due to the different types of raw materials being processed - sheep’s kashkaval and white brined cheese whey (SCWSM 1) and cow’s cheese whey (SCWCM 1). In P2, where curd is produced by means of membrane retention of whey proteins, the reduction of TS exceeds 92%. One of the biggest advantages of membrane technologies over cloth filtration is the ability to retain smaller protein fractions, resulting in cleaner waste streams [7171 Tatoulis T, Tekerlekopouloi A, Akratos C, Pavlou S, Vayenas D. Aerobic biological treatment of second cheese whey in suspended and attached growth reactors. J Chem Technol Biotechnol 2015;90(11):2040-9.]. In support of this statement, the lower amounts of suspended matter in the SCW are visible. Their concentration in SCW2 is over 87% less than that in Plant 1.
The active reaction of SCW is more acidic than whey [7171 Tatoulis T, Tekerlekopouloi A, Akratos C, Pavlou S, Vayenas D. Aerobic biological treatment of second cheese whey in suspended and attached growth reactors. J Chem Technol Biotechnol 2015;90(11):2040-9.]. In the SCW from P2 (SCW2) it reaches 5.81, while for P1 it is about 4.55 pH units.
The higher fat content of sheep's milk is reflected in the quality of the SCW. FOG in SCWSM 1 is 305 mg/L, which is 30 times higher than the permissible values or 59.7% more than the same in SCWCM 1. But not found in SCW2. By retaining milk fats, membrane technologies contribute to shortening the technological steps in the treatment of dairy wastewater [7272 Reig M, Vecino X, Cortina JL. Use of membrane technologies in dairy industry: an overview. Foods 2021;10(2678):1-29.,7373 Birwal P, Deshmukh G, Priyanka SP, Saurabh SP. Advanced technologies for dairy effluent treatment. J Food Nutr Popul Health 2017;1(1:7):1-5.].
Undoubtedly, BOD and COD most strongly influence the selection of appropriate technologies for processing waste streams [7474 Moujdin IA, Summers JK. Promising techniques for wastewater treatment and water quality assessment. IntechOpen; 2020. Emerging trends in wastewater treatment technologies: The current perspective.]. High values of these indicators are found for SCWSM 1 and SCWCM 1, making them available mainly for anaerobic processes [4747 Pires AF, Marnotes NG, Rubio OD, Garcia AC, Pereira CD. Dairy by-products: a review on the valorization of whey and second cheese whey. Foods 2021;10(1067):1-24.]. But COD at SCW2 is only 2500 mg/L and BOD5 is 954 mg/L. Low pollutant concentrations suggest the possibility of using aerobic biological treatment of SCW2 [7373 Birwal P, Deshmukh G, Priyanka SP, Saurabh SP. Advanced technologies for dairy effluent treatment. J Food Nutr Popul Health 2017;1(1:7):1-5.]. However, here BOD5:COD is around 0.38 - below the 0.5 limit for successful aerobic microbial treatment [7575 Srinivas T, 2008. Environmental Biotechnology. New Delhi: New Age International (P) Limited, Publishers; 2008. Water and Wastewater, p. 27.,7676 Chan Y, Chong M, Law C, Hassell D. A review on anaerobic-aerobic treatment of industrial and municipal wastewater. Chem Eng J 2009;155(1-2):1-18.]. Furthermore, nitrogen compounds should be about 1:20 of the biodegradable pollutants [7777 Jördening HJ, Winter J. Environmental biotechnology: concepts and applications. Weinheim: Wiley-VCH Verlag GmbH & Co. KGaA; 2005. Chapter 2, Industrial wastewater sources and treatment strategies; p. 69-70.,7878 Slade AH, Thorn GJ, Dennis MA. The relationship between BOD:N ratio and wastewater treatability in a nitrogen-fixing wastewater treatment system. Water Sci Technol 2011;63(4):627-32.], and here BOD5:N is 119:1. The lack of N in combination with rapidly digestible BOD in the form of lactose can lead to fast development of filamentous microorganisms during wastewater treatment processes. This disrupts the formation and proper separation of activated sludge [7979 Treatment Plant Operators. Wisconsin: Eagle River. COLE Publishing. Optimal nutrient ratios for wastewater treatment. [Internet] 2018 [cited 2023 May 17]; Available from: https://www.tpomag.com/whitepapers/details/optimal_nutrient_ratios_for_wastewater_treatment_sc_001fa
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80 Gutierrez J. Nitrogen deficiency and its effect on floc formation and sludge dewatering. Madison, Wisconsin: Aquafix Incorporated [Internet] 2020 [cited 2023 April 12]; Available from: https://teamaquafix.com/low-nitrogen-effects/.
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-8181 Meniscus. Bulking in the activated sludge process Huntingdon [Internet] 2022 [cited 2023 April 19]; Available from: https://www.meniscus.co.uk/bulking-in-the-activated-sludge-process/.
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]. COD:N is about 312:1, which exceeds the possibilities for normal development of methanogenic bacteria [6464 Frigon JC, Bruneau T, Moletta R, Guiot SR. Coupled anaerobic-aerobic treatment of whey wastewater in a sequencing batch reactor: proof of concept. Water Sci Technol 2007;55(10):201-8.,6565 Zappi M, Fortela DL, Sharp W, Bajpai R, Gang D, Holmes W, et al. Evaluation of the methane production potential of catfish processing wastewater using various anaerobic digestion strategies. Processes 2019;7(368):1-15.]. An analogous conclusion can be drawn for SCWSM 1 and SCWCM 1, where this ratio is even higher.
The TP content in SCW from the different productions is similar. It is highest in SCWSM 1 - 32 mg/L, followed by SCW2 - 28 mg/L and SCWCM 1 - 21 mg/L. The membrane technology implemented in P2 does not help to reduce phosphate compounds in SCW2. This requires a TP separation step before discharge. Efficient biological elimination of TP from SCW2 would be difficult because COD:P = 89:1, about 4.5 times the optimum [8282 Jördening HJ, Winter J. Environmental biotechnology: concepts and applications. Weinheim: Wiley-VCH Verlag GmbH & Co. KGaA; 2005. Chapter 1, Bacterial metabolism in wastewater treatment systems, p. 1-48.]. Here, other possibilities for its removal should be sought [6363 Numviyimana C, Warchol J, Izydorczyk G, Basladynska S, Chojnacka K. Struvite production from dairy processing wastewater: Optimizing reaction conditions and effects of foreign ions through multi-response experimental models. J Taiwan Inst Chem Eng 2020;117:182-9.,8383 Balamane-Zizi O, Aït-Amar H. Combined processes for Phosphorus removal from a dairy plant wastewater: Conditions influencing the chemical process. J Env Sci Technol 2009;2:112-9.,8484 Lavanya A, Thanga RSK. Effective removal of phosphorous from dairy wastewater by struvite precipitation: process optimization using response surface methodology and chemical equilibrium modeling. Sep Sci Technol 2020;56(2):395-410.].
Whey from the production of milk curd and pressed milk
Whey can be obtained from other dairy products [8585 Rocha-Mendoza D, Kosmerl E, Krentz A, Zhang L, Badiger S, Miyagusuku-Cruzado G, et al. Invited review: Acid whey trends and health benefits. J Dairy Sci 2021;104:1262-75.]. In Table 2 the results of an analysis of whey formed during the production of milk curd (MW3) and strained yoghurt milk (SYW3) in P3 are described. Compared to the other types of whey, the amounts of MW3 and SYW3 are less than half of the manufactured milk. Contamination is closer to the SCW from P1. Significant differences are found in BOD, TN and TP content, which are much higher in P3 effluents.
Strained yoghurt production gives 400 L/m3 of milk more SYW3 and more contaminated whey than milk curd processing. The content of TS and TSS is close, with 3.8% more for TS and 5.3% more for TSS in favor of SYW3. Here, the active reaction is weakly acidic - 5.1, while in MW3 - 4.7. FOG is 3 times more in SYW3. It is noteworthy that BOD in MW3 is lower by 7.8%, but COD exceeds the values in SYW3 by about 8.7%. The likely reason is related to the presence of more difficult to oxidize compounds in the whey of milk curd. BOD5:COD varies: 0.54-0.58, but suggests that these waste streams are suitable for biological treatment [7676 Chan Y, Chong M, Law C, Hassell D. A review on anaerobic-aerobic treatment of industrial and municipal wastewater. Chem Eng J 2009;155(1-2):1-18.]. TN reaches 15,990 mg/L for SYW3 and 11,320 mg/L for MW3 and is the highest of all whey samples analyzed. The presence of high concentrations of nitrogen compounds will create a problem in anaerobic fermentation of whey [8686 Wagner AO, Hohlbrugger P, Lins P, Illmer P. Effects of different nitrogen sources on the biogas production - a lab-scale investigation. Mic Res 2012;167(10):630-6.,8787 Grof N, Hutnan M. Anaerobic fermentation of substrate with high nitrogen content. Chem biochem eng quart 2021;35(3):345-53.]. The TP is closer to that in cheese whey, but it is 10 times higher than the same in SCW.
Washing wastewater from the production of kashkaval, white brined cheese, whey and milk curd, yoghurt and strained yoghurt
A large part of the industrial waste streams of the dairy industry is formed by washing waters [8888 Boguniewicz-Zablocka J, Klosok-Bazan I, Naddeo V. Water quality and resource management in the dairy industry. Environ Sci Pollut Res Int 2019;26(2):1208-16.]. According to their purpose, they can be grouped into first wash water (WWI) - after pushing the milk and whey out of the apparatus and second wash water (WWII) - for cleaning the equipment after washing [8989 Andreev A. Shivarov M. Technological equipment in the dairy industry. Sofia: Zemizdat; 1992. Installations for washing the machines, devices and facilities in the dairy industry; p. 188-196. (In Bulgarian)]. In Table 3 the values of pollution of the washing waters from the production of kashkaval, white brined cheese and whey curd from P1 (WWI 1 and WWII 1, respectively) and P2 (WWI 2 and WWII 2, respectively), and yoghurt, strained yoghurt and milk curd from P3 (WWI 3 and WWII 3, respectively) are summarized.
In the most of the cases the amount of washing water exceeds the volume of milk. An exception can be made for WWI 3 where 0.30 m3 wash water is used per 1 m3 milk. The common reason is due to the assortment diversity of the products received and the available production technologies. For P2, the wash flows reach 3.66 m3/m3 milk, followed by P1 - 2.44 m3/m3 milk and P3 - 3.07 m3/m3 milk. Also, the first wash waters are less compared to the second wash waters. The difference is particularly large in P3, where WWI 3 is under 10 % from the total amount of wash water. Here, the main activity is focused on obtaining yogurt, which occupies almost the entire volume of milk, and not only its proteins. While whey are formed only from milk curd and strained yoghurt. Thus, the need for WWI 3 is minimal as large volumes of whey do not need to be pushed out of the respective production vessels.
In the washing waters of cheese and whey curd, TSS exceed 60%. But in the case of yoghurt production - TSS are a little over 10%.
In all plants, the WWI is more polluted than the WWII. The active reaction is above 5. The washing waters from P3 have the lowest pH values - 5.1-5.3, while in P2 they exceed 6.6. FOG are not detected neither in the wash water of P2, nor in WWII 1, but in WWI 3 they are 730 mg/L. In individual streams, BOD5 varies from 400 to 706 mg/L, while COD - 650 to 1590 mg/L. The low pollution of these wastewaters allows application of aerobic treatment methods [9090 Tocchi C, Federici E, Fidati L, Manzi R, VIncigurerra V, Petruccioli M. Aerobic treatment of dairy wastewater in an industrial three-reactor plant: Effect of aeration regime on performances and on protozoan and bacterial communities. Wat Res 2012;46(10):3334-44.]. They can be more accessible for P2 and P3 where BOD:COD is over 0.5 [7575 Srinivas T, 2008. Environmental Biotechnology. New Delhi: New Age International (P) Limited, Publishers; 2008. Water and Wastewater, p. 27.]. For P1, BOD:COD reaches 0.41-0.42 - here it is necessary to use physicochemical processes first before microbial treatment [7676 Chan Y, Chong M, Law C, Hassell D. A review on anaerobic-aerobic treatment of industrial and municipal wastewater. Chem Eng J 2009;155(1-2):1-18.]. In wash waters from P2, no TN is detected, making biological treatment difficult. A possible solution is to enrich these effluents with nitrogen compounds, combine them with domestic waste streams or apply for dilution of highly contaminated dairy wastewaters [9191 Carvalho M, Prazeres A, Rivas J, 2013. Cheese whey wastewater: Characterization and treatment. Sci Tot Envir 2013;445-446C:385-96.]. Wash waters from P1 and P3 are suitable for aerobic treatment. The high concentrations of FOG, TN and TP in P3 require an approach to separate lipids and eliminate biogenic elements from the waters before discharge into water bodies [9292 Broughton A, Pratt S, Shilton A. Enhanced biological phosphorus removal for high-strength wastewater with a low rbCOD:P ratio. Biores Technol 2008;99(5):1236-41.,9393 Balamane-Zizi O, Aït-Amar H. Biological phosphorus removal from dairy wastewater by alternating anaerobic and aerobic conditions. Afr J Biotechnol 2012;11(46):10575-81.].
The results of the analyses are summarized with the production technologies in a unified flow diagram, which can serve as a basis for creating a general model for the more effective treatment of waste streams from the dairy industry in the future (Figure 1).
Simplified flowchart from three Bulgarian dairy multiproduct plants and possible treatment options of derived wastewater streams.
CONCLUSION
Based on the studies carried out, the following more important conclusions can be summarized:
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No significant differences are found in the waste streams from Bulgarian and foreign milk processing plants.
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The most contaminated are the whey from the production of kashkaval and white brined cheese with the raw material - sheep's milk.
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The cleanest effluents are the washing waters, but they fill the largest volume compared to the raw milk.
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Membrane technologies create conditions for a more complete utilization of the whey, but they reduce the possibilities for biological treatment of the wastewaters coming out of them.
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Anaerobic methods are more suitable for treating whey, while aerobic methods - for washing waters.
Whey and washing waters from the production of yogurt, milk curd and strained yoghurt are more loaded with biogenic elements than those from the production of kashkaval and white brined cheese.
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Publication Dates
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Publication in this collection
19 Aug 2024 -
Date of issue
2024
History
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Received
03 Oct 2023 -
Accepted
29 Feb 2024