Effluent generation by the dairy industry: preventive attitudes and opportunities

ENVIRONMENTAL ENGINEERING

Effluent generation by the dairy industry: preventive attitudes and opportunities

V. B. Brião^{I, *}; C. R. Granhen Tavares^II

^IFood Engineering Department, University of Passo Fundo, Phone: (+55) (54) 3316-8490, Fax: (+55) (54) 3316-8455, Campus I. BR 285 km 171, Zip Code 99001-970, PO Box 611, Passo Fundo - RS, Brazil. E-mail: [e-mail]

^IIChemical Engineering Department, University of Maringa, Phone: (+55) (44) 3261-4746, Colombo Avenue 5790. Zip Code 87020-900, Maringá - PR, Brazil. E-mail: [e-mail]

ABSTRACT

Work aimed to identify the effluent is generating areas in a dairy company for purpose of changing concept pollution prevention. methodology consisted measuring volumes and collecting samples effluents production sectors. analysis was conducted by sector, order those which generated excessive amounts effluents. results show that dry products (powdered milk powdered whey) are greatest generators BOD, nitrogen phosphorus, while fluid form (UHT milk, formulated UHT, pasteurized cream) butter produced large quantities oils grease. solids recovery, waste segregation water reuse can be applied with saving potential as much R$ 28,000 ($ 11,200) per month only raw materials also environmental gains in pollution prevention.

Keywords: Dairy; Pollution prevention; Wastewater; Milk.

INTRODUCTION

Of all industrial activities, the food sector has one highest consumptions water and is biggest producers effluents per unit production in addition to generating, besides generate a large volume sludge biological treatment (Ramjeawon, 2000). dairy industry an example this sector, which cleaning silos, tanks, heat exchangers, homogenizers, pipes other equipment, engenders amount with high organic load. load basically constituted by milk (raw material products), reflecting effluent levels chemical oxygen demand (COD), biochemical (BOD), oils grease, nitrogen phosphorus. Moreover, automatic system – CIP (cleaning place) - discards rinse waters pHs varying between 1.0 13.0, further complicating question (Brião, BOD directly related wastes (90% 94% BOD), some cases losses can reach 2% processed (UNIDO, 1999a).

In order to reduce the effects of industrial sector pollutants, end-of-pipe treatment techniques have been improved, at same time prevention measures are being implemented minimize production residues (Metcalf & Eddy, 1991).

End-of-pipe control captures wastewater after its generation, enabling discharge into environment. These are peripheral solutions that focus primarily on the chemical, biological and physical treatment of terminal streams. However, they address symptoms not true causes environmental problems, therefore, cost-effective or sustainable (Khan et al., 2001).

The essential feature of pollution prevention program (P2) is concept "reduction at source", based on idea that generation pollutant can be reduced or eliminated by increasing efficiency in use raw materials, energy, water and other resources (Cagno et al., 2005). Cleaner production intends to integrate aims order reduce quantity toxicity residues discharges terms. source reduction refers any praxis, process technology seeks elimination volume, concentration generating (CETESB, 2004; Figueiredo Santos, 2000; Quaresma Pacheco, 2000). involves negative environmental impacts throughout product's, life cycle, from extraction material its final use. Finally, rationalization every product utilized, it results a savings, producing cheaper consequently more competitive products (UNIDO, 1999a; SENAI, 1998).

The dairy company studied is a multiproduct factory and its wastewater treatment process based on six steps: (a) screening; (b) use of Parshall flowmeter; (c) sandtrap/oil grease separation in tank; (d) flow equalization (e) an activated sludged process; (f) tertiary three facultative lagoons. However, almost overloaded requires more complete diagnosis.

On the other hand, minimization of pollution index indicator must be evaluated, not only in terms final treatment, but also as an opportunity to reduce production costs, by optimizing them and increasing process efficiency profit.

The purpose of this work was to identify operations or processes in which there were opportunities for reducing impacts load and volume effluent treatment at a dairy factory.

MATERIALS AND METHODS

Experiments

The method consisted of evaluating load coefficient and volumetric three macrosectors (which combine production rooms) in a dairy factory. At same time, behavior raw effluent treatment station was also analyzed, so that experiments were conduted over two-month period.

The macro sectors of industry are milk reception, fluid products (UHT milk, formulated UHT, pasteurized cream and butter) dry (powdered powdered whey). An ultrasonic flowmeter was installed, pipelines that supply water for washing tanks, pipes equipment in each sector or process. This measured evaluated terms effluent generated. raw wastewater by Parshall treatment station means sensor associated with on-line integrator (Figure 1). The volume of processed milk in each sector was obtained based on company production reports.

The volumetric coefficient (VC) in each sector was calculated as

where V is the volume of effluent generated (or consumed water) and processed milk. VC unit shown in cubic meters effluents for each meter

The load coefficients (LC) were calculated for four parameters (BOD, nitrogen, phosphorus and oils grease) as

where A is the concentration (mg L"¹), V volume of effluent generated (L) and processed milk (L). LC unit given in milligrams pollutant for each liter milk, or kilograms cubic meter milk.

The pH was also measured in order to identify which sectors have greater effect on raw wastewater.

Analysis

Compound samples were analyzed. These collected one per hour during the processes.

The analytical methods followed were those of American Public Health Association – APHA (APHA, 1991). COD was determine, by a photometric quantification at 600 nm; nitrogen analyzed classic "macro-Kjeldahl" method; phosphorus through acid digestion and quantified vanadomolybdophosphoric oils grease Soxleth gravimetric method pH direct measurement with meter. BOD predicted based on company records it related to COD. This ratio 2.13 (Brião, 2000).

RESULTS AND DISCUSSION

Average Concentration in the Sectors Evaluated

The average pH values for three macrosectors and raw wastewater as well COD concentrations, nitrogen, phosphorus oils grease are shown in Table 1. The average values for the parameters, which are found in Table 1, do not indicate an excessive discharge load in the treatment system. However, the high standard deviations show that there was a large variation in the parameters evaluated.

Figure 2 illustrates an example of this variation in discharge load; it shows the evolution of COD over the time during which the evaluation was performed. It is possible to identify several peeks, showing that some operations discharge excessive loads on specific days even though they fall within the average values. Figure 3 shows the nitrogen concentration of streams evaluated whilst Figure 4 shows the phosphorus concentration of the same streams. Both figures show a similar behavior for COD; the average concentration is near the lowest acceptable value for treatment in a biological system. However, there are operations discharging excessive organic matter that could overload the treatment system.

Special attention should be given to the 16th (sixteenth) day, on which highest value of COD was obtained. this spray dryers used in production powdered milk and whey were cleaned, discharging a high load into wastewater treatment system. However, cleaning occurs once every twenty days. reception peaks (days 3 8) obtained rainy days, when trucks arriving at platform covered with clay mud, had an effect value. station has sand trap as first step primary treatment, so there are no negative consequences average for fluid dairy factory is not considered critical (Table 1), but high the effluent value on day 13 shows a clear effect on the raw wastewater, which is attributed to the formulated UHT chocolate milk (a brown color in the sample) production wastes. For the dry products, the average COD value was about 2091 mg L^-1.

The increase in raw wastewater COD on tenth day was related to CIP solutions discharged by evaporators dry products sector (acid and alkaline solutions).

The behavior of pH is shown in Figure 5. Most of streams had of pH elevated values with an average value the raw wastewater of about 10.45 that reaches the station. This is explained by the alkaline cleanings of the CIP system. The alkaline cleanings aim at general fat saponification and removal of organic material. However, the alkaline cleanings are done with greater frequency (at the end of each production cycle), while the acid solutions are circulated once a week. The effects of acid solutions can be verified on days 5, 10 and 16, when a low pH in some sectors. Although, even when the acid cleaning was carried out, the small effect of pH did not reflect a drastic reduction in pH in the raw effluent.

Volumetric Coefficients

Table 2 shows the volumetric coefficients for from milk reception, fluid products, dry products and the raw wastewater.

There is great disagreement among references as to the general volumetric coefficient for industry (represented by raw wastewater), since are many differences between industrial processes and procedures each production sector. Veysseyre (1988) points out that in factories which produce several milk products, liter of 7 10 liters wastewater generated. Braile Cavalcanti (1993) report area product elaboration final packaging biggest sources effluents industry. They add washing waters correspond same volume processed milk, process products had a 1.1 6.8 milk. Byylund (1995) reports typical coefficients near 2.5 water but economizing 1.0 per can be achieved. 1986, Carawan (1996) analyzed United States America he found an average 4 milk; author added savings, less than consumed obtained.

The results of this work show that volumetric coefficient industry evaluated is not high. However, UNIDO (1999a) indicates with good management programs up to 0.5 cubic meter effluents can be achieved for each processed milk effluents. value serve as a reference water consumption and generation on minimizing. Thus, if an effluent minimization program implanted, difference between 0.666 would represent savings almost 25% in consumption, percentage which possible according Carawan Stengel (1996), who reported effective pollution reduction programs, decrease achieved.

Load Coefficients

Table 3 shows the BOD coefficients obtained in this work and the coefficients reported by other authors. It can be observed that the load coefficients of the company evaluated are smaller than the values found in the literature (except the powdered milk and powdered whey production sector – dry products). Some industry waste values that reach 12 kilograms of BOD per cubic meter of processed milk with more than 90% of this BOD resulting from milk loss and with a reduction in wastewater, can be reduced to 1.0 kg of BOD per cubic meter of processed milk (Poester and Leitão, 1989).

The data presented in Table 3 show that the organic load discharged by the milk reception is not excessive, being about ten times smaller than the value for raw effluent. On the other hand, the processing is responsible for the high values of raw effluent organic load, a fact also reported by the authors cited.

In Table 4 the nitrogen, phosphorus and oil and grease coefficients for the three sectors and of the raw wastewater are shown. An evaluation of Tables 3 and 4 demonstrates that there is a equilibrium between the BOD coefficients and other pollutants. The ratio of BOD to nitrogen was between 12 and 18. In the same way, the ratio of BOD to phosphorus was found to be between 20 and 36, indicating a good nutritional ratio that goes into the biological treatment unit. On the other hand, high values of both pollutants can resulting excess on treated effluent, since there is a nitrogen and phosphorus removal limit with this kind of treatment.

Table 5 contains the total values of pollutants discharged monthly into the treatment system. It can be observed that milk reception contributed only 10% of the total BOD. The sector which discharged most BOD, nitrogen and phosphorus was the dry products sector, while the fluid products was the sector most responsible for oil and grease emission.

According to Carawan (1996), each kilogram of effluent BOD corresponds nine kilograms milk lost during the process. Thus, adding stream BODs, it is seen that about 28000 kg entered treatment system per month, corresponding 252000 liters by industry. This amount near 0.7% total received industry, which processes 36 million month. value not a bad result. Kirsh and Looby (1999) report as much 2% processed can be processing. However, UNIDO (1999a) relates good waste management programs achieve losses 0.5%. difference between 0.5% would mean almost 72000 month revert back company's account instead being discharged into sewers. If taken raw material costs around R$ 0.40 (forty Brazilian cents) or $ 0.16 (sixteen US more than 28,000.00 (twenty eight thousand reais) - 11,520 recovery only in material.

According to Carawan and Stengel (1996), effective waste management programs can reduce BOD as much 33%. This would be about 9200 kg of per month, consequently, 83,000 liters milk, the previously estimated approximate value.

PREVENTIVE ATTITUDES

The action proposed is twofold: (1) a reduction in water consume and (2) minimization of organic load.

Cleaning by means of the CIP system and reuse recycling water are examples processes which reduce volumetric coefficient. In reference to this topic, it must be reported company installed system, minimizes consumption, most part processes; however, there were some exceptions, such as a few trucks that not adapted with "spray bowl" for washing system. addition, spray dryer was operated manually rather than automatically, consumed large amounts water.

Water reuse and recycling was a reality in the company. Many processes, such as centrifugal separation with cooling closed circuit recycled water. filling machines (for UHT milk packaging) were cooled recovered evaporated (from evaporator for production of powdered milk) used cleaning trucks outside floors. retentate from reverse osmosis system (used desalination boiler feedwater) mixed into supply reservoir. Figure 6 the sectors where these measures were implemented and the percentage of each to total wastewater are shown. The effluent considered water consumption while the water evaporated in the boiler and cooling towers was not computed in the material balance in Figure 6. The sum of these preventive actions account for a 10% decrease in total wastewater generated.

The company also took action to reduce of effluents loads, which is reflected by low BOD, nitrogen, phosphorus and oil grease coefficients. actions taken were separation discharged milk automatic ejection sludge in centrifugal separators; segregation whey from butter for use animal feed; recirculation first rinse water evaporators (which has a high total solids level) at beginning process, reducing organic load fluids dry products.

In spite of the great concern company to minimize waste, there were still opportunities for reduction previous coefficients. recovery solids first rinse could be a pollution prevention action. are examples milk recovered by use membrane separation processes (reverse osmosis) used production ice cream and desserts. Three direct results obtained: minimization impact effluent generated; casein reuse permeated stream, which is high quality enough drinking water (Water, 1996). central system treatment these waters installed, recovering solids, mainly from reception fluid products sector.

In Table 5 it can be seen that fluid products is sector most responsible for the emission of oils and grease. This is the direct result of the production of pasteurized cream and butter, which generates effluents with high values for this parameter. In this case, the simple separation of the first rinse water and its use for animal feed would be beneficial in the reduction of organic load. The same procedure could be installed in the manufacture of UHT formulated products. Once again, the membrane separation process was shown to be a promising alternative to the recovery of nutrients found in the effluents. Skelton (2000) reported on grease recovery in margarine processing, which can be reapplied in this process.

"Dry cleaning" is utilized frequently in other food industries, such as the bakery industry (Carawan, 1999) and shrimp processing 1996a). It could be adapted to spray dryers for scratching/or sweeping of adhered powdered milk preceding first flush, which would remove a large part solids adhering equipment. This operation more attractive use old equipment, cleaned manually. These added reservoir that receives rinse.

Membrane technologies have been applied successfully to reclaim the effluent that evaporates in evaporator. some cases, use of permeated into drinking water or even boiler feedwater is possible (Mavrov and Bélières, 2000; Mavrov et al., 2001; Novalic 1998). On days with high production powdered milk whey, large amounts these effluents were generated, so cleaning trucks floors external did not all effluent, which was thus discharged. Energetic benefits can also be obtained this water, since it discharged at 55-60ºC an integrated system (Figure 7). This water could warm up the boiler feedwater by means of heat exchangers (generating a savings of fuel oil) and could be used as make-up water for cooling towers, which do not require excellent quality in terms of organic content.

The discharge of CIP solutions after a long period use is common praxis in dairy industry. result its negative effect can be observed Figure 2, an effluent with pH values which vary from about 2.0 to 13.0. Processes with ultrafiltration and nanofiltration membranes have been studied for regeneration of these solutions, keeping the organic load and continuing use of the solutions (Novalic et al., 1998a; Trägardh and Johansson, 1998). However, a careful economic study aiming to evaluate this possibility must be done.

CONCLUSIONS

Sectors of dairy production are big pollutors. Effluents from the fluid and dry products present environment risks if not properly evaluated treated, preventive programs can reduce volume emissions organic load, decreasing costs end-of-pipe treatment.

Several measures were taken by the company studied to reduce water consumption and organic load, resulting in coefficients that lower than those other references. However, preventive could be studied:

The treatment of the water that evaporated in the production of powdered milk by the membrane separation process is a great opportunity to reclaim water, although the investment costs are still high. Only this action could reclaim nearly 10% of the total fresh water. Besides, energetic gains could be achieved with the installation of a reverse osmosis system;

The installation of tanks to separate the first rinse water is a cheap alternative for reducing the load coefficient; the content of these tanks could be used for animal feed;

Another way to reduce the organic load could be to install a reverse osmosis system to reclaim milk solids from the first rinse water in equipment and pipe lines; in addition, the retentate could be used for other milk products and the permeate as boiler feed water;

"Dry cleaning" with a spray dryer is a good opportunity to separate milk solids, thereby avoiding washing them out at the treatment station.

Lastly, the installation costs of any process will be variable, which can hinder minimization effluents and reduction organic loads.

NOMENCLATURE

A

Concentration of pollutant

g m^–³>

BOD

Biochemical oxygen demand

mg L^–¹>

CIP

Cleaning in place

dimensionless>

COD

Chemical oxygen demand

mg L^–¹>

LC

Load coefficient

kg pollutant m^–³ milk>

P2

Pollution prevention

dimensionless>

UHT

Ultra-high temperatures

dimensionless>

v

Processed milk volume

m³>

V

Effluent volume

m³>

VC

Volumetric coefficient

m³ effuent m^–³ milk>

(Received: March 20, 2006 ; Accepted: September 2, 2007)

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Publication Dates

• Publication in this collection
  12 Feb 2008
• Date of issue
  Dec 2007

History

• Accepted
  02 Sept 2007
• Received
  20 Mar 2006