VOLATILE FATTY ACIDS (VFA) CONCENTRATION IN WASTEWATER FROM DIFFERENT SECTIONS OF DAIRY INDUSTRY

Wojciech Janczukowicz, Marcin Dębowski, Marcin Zieliński, Jarosław Pesta
Department of Environment Protection Engineering, University of Warmia and Mazury in Olsztyn, Poland

ABSTRACT

The aim of the study was to determine volatile fatty acids (VFA) concentration in wastewater from different sections of the dairy industry. Wastewater was collected from outlets of all sections of dairy industrial plant. Cottage cheese whey and cheese whey composition were analysed. The highest volatile acids concentration was obtained in cottage cheese whey. The average concentration was 792.1 ± 247.1 mg CH₃COOH · dm^-3. Cheese whey, wastewater from cottage cheese section and cheese section contained over 230 mg CH₃COOH · dm^-3. In wastewater from other sections of dairy industry the concentration of VFA was not high. Quality research of wastewater revealed that independently on the sources of VFA, acetic acid was the most abundant. The contribution of the other acids, as iso-butyric, valeric, iso-valeric and caproic, did not exceed 7 % of the total VFA concentration.

Key words: dairy wastewater, volatile fatty acids (VFA), cheese whey.

INTRODUCTION

Dairy wastewater treatment needs to provide high effective systems of carbon, nitrogen and phosphorus compounds removal. It results from wastewater composition [2, 3] and the requirements as for treated food industry wastewater [8].

In activated sludge tanks where carbon removal, nitrification, denitrification and enhanced biological phosphorus removal take place (EBPR), the effectiveness of the last two processes depends on the accessibility of easily biodegradable organic compounds. The organics are used by poly-accumulated bacteria under anaerobic conditions but also at nitrate/nitrite reduction to gas nitrogen by denitrifying microorganisms. Moreover, form of organic substrate and its biodegradability determine the rates of denitrification and dephosphatation. During stirring stage in SBR reactor volatile fatty acids (VFA), presented in wastewater, are used at nitrate reduction to gas nitrogen under anoxic conditions, but also at metabolic processes of polyphosphate-accumulated microorganisms under anaerobic conditions [10, 11, 12, 13].

Volatile fatty acids can be found in the reactor influent or be generated during fermentation, that takes place directly in the reactor stirring phase. The rates of both processes are different. VFA assimilation is more efficient than fermentation [4, 13]. Because of that, nitrates and orthophosphates removal is more effective if wastewater contained higher amount of volatile fatty acids. Wastewater rich in VFA may improve high poly-beta-hydroxybutryrate (PHB) storing by polyphosphate-accumulating bacteria.

The aim of the study was to determine volatile fatty acids (VFA) concentration in wastewater from different sections of the dairy industry.

MATERIALS AND METHODS

Wastewater was collected from outlets of all sections of a dairy industrial plant. Characteristic of the dairy factory is presented in table 1. Cottage cheese whey and cheese whey composition were analysed. Samples of wastewater were taken one time a month in the period from September 2003 to August 2004. Wastewater samples at the volume of 2.0 dm³ were taken every half an hour during working hours of the dairy from 6³⁰ a.m. to 2³⁰ p.m. (17 samples). Wastewater was collected in vessels kept and transported in the temperature of 4°C.

Table 1. Amount of milk processed and water used connected with production process

Average amount of milk processed	7.8 mln dm3/year
Averade water used per year	11000 m3/year
Averade water used per day	20 m3/day – 65 m3/day
Production	milk, butter, cheese, cream, yoghurt, kefir

Wastewater used in the experiment comes from the following processes:

• wastewater from milk reception point – generated due to cisterns, lines, floors and approach roads washing. This wastewater is similar to diluted milk.

• wastewater from apparatus room – generated due to washing of centrifuges, devices used for thermal milk processing, devices for homogenization, concentration and degassing. Composition of this kind of wastewater depends on washing chemical agents used.

• wastewater from butter section – generated due to washing of rooms, devices and installations for butter production. Wastewater contains high concentration of fats.

• wastewater from cottage cheese section – generated due to washing of rooms, devices and installations for cottage cheese production. Wastewater contains high concentration of organic compounds.

• wastewater from cheeses section – generated due to washing of rooms, devices and installations for cheese production. Wastewater contains high concentration of organic compounds.

• cheese whey – waste product after cheese production (sweet whey).

• cottage cheese whey – waste product after cottage cheese production (sour whey).

• mixed wastewater – mixture of all kinds of wastewater generated in the dairy collected to one stream (wastewater from pumping station).

During the study quantity content of volatile fatty acids was determined. Chromatographic analysis of volatile fatty acids were performed by means of gas chromatograph HP 6890 equipped with a flame ionization detector FID, Innowax capillary column (60 m × 0.25 mm i.d., 0.50 µm liquid film thickness). Detector temperature and injector port temperature were 280°C and 250°C. Column temperature was 160°C. Helium was used as a carrier gas at flow rate 2 ml/min (with a injector port at split 1:50).

Samples of wastewater at volume of 1.5 ml were diluted with 50 µl of phosphoric acid and left for the whole night in the refrigerator. Next day the samples were centrifugalize for 15 min (15.0 G).

During the study quantity content of volatile fatty acids was determined. Chromatographic analysis of volatile fatty acids were performed by means of gas chromatograph HP 6890 equipped with a flame ionization detector FID, Innowax capillary column (60 m × 0.25 mm i.d., 0.50 µm liquid film thickness). Detector temperature and injector port temperature were 280°C and 250°C. Column temperature was 160°C. Helium was used as a carrier gas at flow rate 2 ml/min (with an injector port at split 1:50).

Samples of wastewater at volume of 1.5 ml were diluted with 50 µl of phosphoric acid and left for the whole night in the refrigerator. Next day the samples were centrifugalize for 15 min (15.0 G).

Statistical analysis of the obtained results was done using variance analysis, at the assumpted accuracy level (p < 0.05). Normal distribution was confirmed by Szapiro – Wilk test, and hypothesis concerning variance homogeneity inside the groups were verified on the basis of Leveney’s test. Analysis of the differences between means from the particular groups was done using Tukey’s test.

RESULTS

Wastewater from milk reception point
Total concentration of volatile fatty acids in wastewater originated from cars washing at milk reception point was in the range from 2.6 mg · dm^-3 to 106.3 mg CH₃COOH · dm^-3, averagely 52.8 ± 34.0 mg CH₃COOH · dm^-3 (Fig. 1). Acetic acid contributed from 51.4% to 100%, propionic acid from 3.85% to 35.9%, and butyric acid from 1.6% to 19.26% of the total quantity amount of volatile fatty acids. Acetic acid appeared to be the most abundant acid because at was present in all eight tested samples of wastewater, and propionic and butyric acids were identified at five and two samples, respectively. In a single sample iso-butyric acid (about 4.7 %) and iso-valeric acid (6.7 %) were detected (Table 2). Caproic acid and valeric acid were under detection level.

Fig. 1. VFA concentration in wastewater from different sections of dairy industrial plant

Wastewater from apparatus room
Volatile fatty acids concentration in wastewater form apparatus room was ranging from 42.0 to 267.6 mg CH₃COOH · dm^-3, the average value was 109.9 ± 63.0 mg CH₃COOH · dm^-3 (Fig. 1). Similarly as for wastewater from milk reception point acetic acid was the major of volatile fatty acids and maid up from 70.5% to 100% of the total amount. Propionic acid content decreased to 66.4% and butyric acid to 8.9% of VFA (Table 2). Acetic acid was present at all eight tested samples of wastewater, and propionic and butyric acids were detected at six and four samples, respectively. The lowest content was obtained for iso-valeric acid (1.1%). There were no contents of iso-butyric, valeric and caproic acids in tested samples of wastewater from apparatus room.

Table 2. Percentage contribution of VFA in dairy wastewater

Wastewater from butter section
The concentration of volatile fatty acids in wastewater from butter section was in the range from 24.6 to 179.2 mg CH₃COOH · dm^-3, averagely 61.2 ± 41.7 mg CH₃COOH · dm^-3 (Fig. 1). Dominant was acetic acid that contributed from 47.6% to 94.5% of total content of VFA. The second major acid was butyric with a percentage contribution on the level from 5.5% to 43.7%. Propionic acid contributed from 7% to 27 % of the total volatile fatty acids concentration. Acetic acid was again the most common acid and was present at eight samples of wastewater from butter section, the same for butyric acid, propionic acid was detected at four samples. In a simple sample of wastewater iso-butyric and iso-valeric acids were present, about 4.4% and 7.2%, respectively (Table 2). Caproic and valeric acids were under detection limit.

Wastewater from cottage cheese section
Total volatile fatty acids concentration was ranging from 96,3 to 422 mg CH₃COOH · dm^-3, the average value was 245.8 ± 99 mg CH₃COOH · dm^-3 (Fig. 1). Acetic acid appeared to be the most abundant acid and it made up from 53.2 % to 98.4 % of the total VFA concentration (Table 2). Lower concentration was obtained for propionic acid (from 1.6 % to 7.9%) and butyric aid (from 0.7 % to 40.8 %). Acetic and propionic acids were detected at all seven samples of wastewater from cottage cheese section, however butyric acid was present at five samples. At simple analysis iso-butyric acid (0.6 %) was measured. There were no contents of iso-valeric, valeric and caprioc acids in tested samples of wastewater.

Wastewater from cheese section
Volatile fatty acids concentration was in the range from 85.3 to 478.8 mg CH₃COOH · dm^-3, averagely 236.3 ± 117.1 mg CH₃COOH · dm^-3 (Fig. 1). Presence of VFA in wastewater from cheese section can be the result of the particular step during cheese production – “grain drying” when intensive increase in acetic microflora concentration take place that favour lactic fermentation.

Acetic acid was the dominant and contributed from 52.6 % to 98.6 % of the sum of VFA. Propionic and butyric acids made up from 0.9 % to 11.5 % and from 0.5 % to 37.8 % of VFA, respectively (Table 2). Above mentioned acids were detected in all samples of wastewater from cheese section. One sample contained iso-valeric and caprioc acids on the level of 1 % of total VFA concentration. Iso-butyric and valeric acids were under detection limit.

Cheese whey
The concentration of volatile fatty acids was in the range from 53.6 to 623.1 mg CH₃COOH · dm^-3, the average value was 299.9 ± 157 mg CH₃COOH · dm^-3 (Fig. 1). Similarly to pervious kinds of wastewater from dairy industry, in most samples of wastewater there was the highest concentration of acetic acid, it made up from 46.1 to 100% of total VFA. As for others, propionic acid made up from 1.7 % to 17.3 %, butyric acid from 0.1 % to 52.2% of VFA. Acetic acid was present at all tested samples of wastewater. Propionic and butyric acids were found at five per eight samples. At single sample iso-valeric acid was detected on the level 0.3 %, and caproic acid on the level 1.5 % of total VFA (Table 2). The concentration of valeric and iso-butyric acids were under detection level.

Cottage cheese whey
Volatile fatty acids concentration was ranging from 448.8 to 1196 mg CH₃COOH · dm^-3, averagely 792.1 ± 247.1 mg CH₃COOH · dm^-3 (Fig. 1). Acetic acid appeared to be the most abundant acid and it contributed from 77.7 % to 97.9 % of total VFA concentration. Propionic acid made up from 1.4 % to 16.2 %, however butyric acid made up from 0.7 % to 22.3 % of VFA (Table 2). Acetic and propionic were measured at all tested samples, butyric acid was present at five per eight samples of wastewater. One sample contained 1.4 % of iso-butyric acid. There was no content of valeric, iso-valeric and caproic acids.

Mixed wastewater
Volatile fatty acids concentration wastewater from pump station was in the range from 38.3 to 181.5 mg CH₃COOH · dm^-3 and the average value was 92.0 ± 39.2 mg CH₃COOH · dm^-3 (Fig. 1). Acetic acid made up from 42 to 100%, propionic acid from 9.6 % to 27.3%, and butyric from 1.2 % to 58% of total VFA content. At all tested samples acetic acid was measured at detectable level, propionic acid was present at five per seven samples. Iso-butyric (1.8 %), valeric (4.1 %) and iso-valeric (3.7 %) acids were detected once (Table 2). Caproic acid was under detection.

DISCUSSION

Presented study revealed that volatile fatty acids concentration in wastewater from different sections of dairy in most cases was higher than at municipal wastewater where VFA content averagely was 60 mg CH₃COOH · dm^-3 [7]. Merely wastewater from milk reception point characterized by lower VFA concentration on the level 52.8 mg CH₃COOH · dm^-3. Taking into consideration that orthophosphate concentration in the influent wastewater gaining pump station was averagely 20.74 ± 8.89 mg P_PO4 · dm^-3, and that according to the literature date effective phosphorus removal at technical conditions needs to provide 4.0 mg CH₃COOH per 1 mg P_PO4 [1], it can be concluded that if the initial nitrate concentration was zero, VFA concentration would be enough to perform dephosphatation in SBR reactor.

The average volatile fatty acids concentrations in wastewater from cheese and cottage cheese section were 236.3 ± 117.1 mg CH₃COOH · dm^-3 and 245.9 ± 99.9 mg CH₃COOH · dm^-3, respectively. It indicates on the possibility of high VFA production in dairy wastewater. Similar conclusion could be found at Danalewich [5] study under dairy wastewater in USA. However, percentage contribution of the particular acids in the sum of volatile fatty acids in case of mixed wastewater from the dairy was different than at American diaries. In presented research it was proved that acetic acid contributed to 72.5%, propionic 11.2%, and butyric 15.2% of VFA content. In American dairy wastewater there was higher acetic acid concentration at the level 83% of total VFA, however there was much lower concentration of butyric acid (2 %), propionic acid was at the same level.

Volatile fatty acids generation relates to fats, peptides, and carbohydrates transformation mainly to acetic acidand other acids, however during fermentation nutrients content in wastewater change insignificantly. For that reason, analyzing usefulness of wastewater from different sections of dairy industry and both whey to volatile fatty acids generation, we have to take into consideration loading of nutrients provided into the fermentor. It could be expected that the nutrients content in the fermentor effluent would not change. Besides VFA as desirable products, nitrogen and phosphorus could be detected. Using fermented wastewater as an external carbon source in the SBR reactor – exactly because of the fact of presence of nutrients in wastewater – could be ineffective action.

Analysis of wastewater from different sections of the dairy revealed that this is the possibility of separate biological treatment in EBPR reactors. This means that dairy wastewater separation from the main stream of wastewater leading to treatment plant do not bring any problems with achievement of the appropriate quality effluent as for carbon, nitrogen and phosphorus compounds. Separation of any kind of wastewater, in order to expose on fermentation that let to obtain high volatile fatty acids concentration, and next supplying it into the SBR reactors, may improve the effectiveness of carbon and nitrogen removal.

It seems to be important to take into consideration the possibility of fermentation only part of wastewater generated at the dairy area, and afterwards supplying them into the SBR reactor at the beginning of the stirring stage. During fermentation volatile fatty acids can be produced not only from proteins, and carbohydrates but also from fats. Hydrolysis, acidogenesis and acetogenesis of fats are not highly effective, and for that reason volatile fatty acids generation from fats in a separated fermentation tank would be more efficient than direct VFA production in SBR reactor. It is related with providing longer time for the process, optimal condition (temperature, pH), and generation of specific biomass responsible for VFA production. These conditions will favour more effective volatile fatty acids generation from carbohydrates and proteins. This is the result of the presence of biodegradable substrates in wastewater that are not accessible for the direct use in biological phosphorus removal, but could be use for VFA production during fermentation [6]. At such wastewater treatment plant part of the influent would be lead directly into SBR reactor, and the stream of wastewater from selected section, with the highest possibility of volatile fatty acids generation, would be supplied into the bioreactor where VFA production would take place.

Concurrently, the quality research of VFA content in wastewater revealed that independently on the sources of VFA, acetic and butyric acids were the most abundant acids. The contribution of the other acids (iso-butyric, valeric, iso-valeric, and caproic acids) did not exceed some percent. During fermentation of wastewater from the different sections of the dairy, describing correlation between the contribution of acetic, butyric and propionic acids, can change, however the concentration of other four acids in wastewater after fermentation is not high. According to Barnard [1] acetic, butyric and propionic acids are mostly presented in the effluent from the reactors for VFA production.

CONCLUSIONS

The highest volatile acids concentration was obtained in cottage cheese whey. The average concentration was 792.1 ± 247.1 mg CH₃COOH · dm^-3. Cheese whey, wastewater from cottage cheese section and cheese section contained over 230 mg CH₃COOH · dm^-3. In wastewater from other section of dairy industry the concentration of VFA was not high.

Quality research of wastewater revealed that independently on the sources of VFA, acetic acid was the most abundant, and its contribution was from 69.3 % in wastewater from butter section to 90.1 % in wastewater from apparatus room. Propionic acid contributed from 5.1% in wastewater form cottage cheese section to 14.2% in wastewater from apparatus room. The average content of butyric acid was from 2.6% of total VFA in wastewater form milk reception point to 22.7 % in wastewater from butter section. The contribution of the other acids, as iso-butyric, valeric, iso-valeric and caproic, did nit exceed 7% of total VFA concentration. In wastewater from pump station acetic acid made up almost 72.5%, propionic acid – 11.2%, and butyric acid – 15.2% of total VFA content.

REFERENCES

1. Barnard J.L., 2000. Projektowanie procesów fermentacji wstępnej. [Projecting of preliminary fermentation process]. Materiały seminarium szkoleniowego “Filozofia projektowania a eksploatacja oczyszczalni scieków”; Lem Projekt; Kraków; 61-76; [in Polish].

2. Bartkiewicz B., 2002. Oczyszczanie scieków przemysłowych. [Industrial wastewater treatment]. Wydawnictwo Naukowe PWN; Warszawa; [in Polish].

3. Chudzik B., 1997. Oczyszczanie scieków z małych rzezni i mleczarni. [Wastewater treatment from small abattoirs and dairy industry]. Przemysł a srodowisko; Warszawa; [in Polish].

4. Daigger G.T., Waltrip G.D., Romm E.D., Morales L.M., 1988. Enhanced secondary treatment incorporating biological nutrient removal. J.WPCF; 60:1833-1842.

5. Danalewich J.R., Papagiannis T.G., Belyea R.L., Tumbleson M.E., Raskin L., 1998. Characterization of dairy waste streams, current treatment practices and potential for biological nutrient removal. Wat. Res.; 32: 3555-3568.

6. Henze M., Harremoes P., 1992. Characterization of wastewater. “Chemical water and wastewater treatment II”; 5^th Gothenburg Symposium; Nice; 313-328.

7. Klimiuk E., 1998. Kinetyka przemian zwiazków azotu i fosforu w osadzie czynnym w warunkach beztlenowo-tlenowych. [Kinetics of nitrogen and phosphorus compounds transformation in activated sludge in anaerobic – aerobic conditions]. Rozprawy i monografie; Wydawnictwo ART; Olsztyn; [in Polish].

8. Rozporzadzenie Ministra Srodowiska z dnia 24 lipca 2006 r. w sprawie warunków, jakie należy spełnić przy wprowadzaniu scieków do wód lub do ziemi, oraz w sprawie substancji szczególnie szkodliwych dla srodowiska wodnego (Dz. U. Nr 137, poz. 984)

9. Wentzel M.C., Dold P.L., Ekama G.A., Marais G.V.R., 1985. Process and modeling of nitrification, denitrification and biological excess phosphorus removal systems – a review. Water Sci. Technol.; 17: 55-71.

10. Wentzel M.C., Ekama G.A., Dold P.L., Loewenthal R.E., Marais G.V.R., 1989. Enhanced polyphosphate organism cultures in activated sludge systems. Part 1: Enhanced culture development. Water SA; 14: 81-92.

11. Wentzel M.C., Ekama G.A., Loewenthal R.E., Dold P.L., Marais G.V.R., 1989. Enhanced polyphosphate organism cultures in activated sludge systems. Part II: Experimental behavior. Water SA, 15: 71-88.

12. Wentzel M.C., Ekama G.A., Marais G.V.R., 1992. Process and modeling of nitrification, denitrification and biological excess phosphorus removal systems – a review. Water Sci. Technol.; 25: 59-82.

13. Wentzel M.C., Loewenthal R.E., Ekama G.A., Marais G.V.R., 1988. Enhanced polyphosphate organism cultures in activated sludge systems. Part I: Enhanced culture development. Water SA; 14: 81-92.

 

Accepted for print: 29.01.2007

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Wojciech Janczukowicz
Department of Environment Protection Engineering,
University of Warmia and Mazury in Olsztyn, Poland
Prawochenskiego 1, 10-957 Olsztyn, Poland
Phone: (089) 523 32 57
email: jawoj@uwm.edu.pl

Marcin Dębowski
Department of Environment Protection Engineering,
University of Warmia and Mazury in Olsztyn, Poland
Prawochenskiego 1, 10-957 Olsztyn, Poland

Marcin Zieliński
Department of Environment Protection Engineering,
University of Warmia and Mazury in Olsztyn, Poland
Prawochenskiego 1, 10-957 Olsztyn, Poland
Phone: (089) 523 32 57
email: marcin.zielinski@uwm.edu.pl

Jarosław Pesta
Department of Environment Protection Engineering,
University of Warmia and Mazury in Olsztyn, Poland
Prawochenskiego 1, 10-957 Olsztyn, Poland

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