M.A. ESIN, A.V. ROMASHKO

1. Esin Mikhail Anatolievich, Head of Process Department, MY PROJECT JSC, floor 8, bld. 7, B. Strochenovsky Lane, Moscow, Russia, 115054, tel.: 8(985)178-65-78, e-mail: yesin@myproject.msk.ru

2. Romashko Andrei Vasilievich, leading engineer of process department of MY PROJECT JSC, floor 8, bld. 7, B. Strochenovsky Lane, Moscow, Russia, 115054, tel.: (495)989-85, e-mail: romashko@myproject.msk.ru

This paper describes the sources of wastewater generation in the production process at dairy enterprises and throws light on the best available technologies for wastewater treatment. The options for their purification have been clarified both before the requirements of discharge into the urban collector and into the fishery reservoir of the highest category. The high operating efficiency and reliability of the flotation units supplied by MY PROJECT are shown in treatment of wastewater from food industry enterprises; the design features of the flotation units are described.

Key words: milk, wastewater, project, coagulant, flocculant, pressure flotation, flotation unit, nitri-denitrification.

Tightening of sanctions imposed on water users (water service companies) for discharge of insufficiently treated wastewater into the water body, inevitably leads to an increase in control over the quality of wastewater discharged by industrial enterprises into the municipal sewage system. This is due to the fact that in the case of treatment of wastewater with waste concentrations of 1.5 to 3 times higher than the maximum permissible concentration for admission to the municipal sewerage network, the operational staff of the wastewater treatment plant do not stand a chance of preventing the discharge of insufficiently treated sewage into the water body.

At the same time, sanctions imposed on industrial enterprises for the discrepancy of the quality of discharged wastewater are incommensurably lower in respect to MPC requirements than on water service companies. This legal discrepancy cannot exist for a long time, therefore there are weighty assumptions that industrial enterprises will in the near future face a more stringent policy in the field of rational use of water resources and prevention of environmental pollution. At the first stage, this can be expressed in the constant monitoring of the quality of wastewater discharged by industrial enterprises to the municipal sewer, by installing automatic samplers and COD, nitrogen and phosphorus compounds analyzers, etc. on the discharge pipeline. The second stage may significantly increase the penalties for exceeding the discharge standards by industrial enterprises. And if we consider that it is impossible to modernize the local wastewater treatment of any industrial enterprise in a short period of time, it is necessary to start acting today.

A distinctive feature of 2011 for our company was a significant increase in the number of requests for the development of technical and commercial offers for dairy enterprises. Treatment of wastewater from these enterprises have many specific features: it is possible to achieve MPC only by using the most efficient equipment.

Ecopolymer has been working with the dairy enterprisers since 1999-2000, when the first aerator system was installed at the enterprise of Nestle Group in Shanghai, China. Since that time the company has accumulated a lot of knowledge in the field of wastewater treatment of the dairy industry and is now ready to offer the most demanding customer integrated solutions for wastewater treatment plants on a turn-key basis: starting with pre-design works and ending with commissioning, staff training and subsequent maintenance.

We shall consider the most typical dairy production process and the nature of the generated wastewater.

The most polluted industrial wastewater comes from such shops as canning, whole milk, whole milk substitutes, as well as washing platforms for milk transportation vehicles. Flows at the dairy industry can be conventionally divided into highly concentrated, coming from the whole milk, canning and whole milk substitutes shops, and low-concentrated - from washing machines and equipment, boiler room and garages. The latter also includes domestic wastewater from buildings and structures located on the territory of the enterprise.

The dairy enterprises can be divided into two groups, based on the requirements for the quality of wastewater treatment and their point of discharge:

1) intracity enterprises discharging treated wastewater to the municipal sewer;

2) those discharging treated wastewater to a water body.

In this connection, various process treatment solutions are used: local treatment for the first group and a complete treatment cycle for the second group. In most cases, it is impossible to separate and treat the wastewater of an individual shop, therefore a mixture of industrial and household wastewater is supplied to the local treatment facilities. Their local treatment in this case consists in filtering on screens with a bar spacing of 2-3 mm, equalization and induced air reagent flotation, which is the most effective method of removing suspended solids, oils and fats from wastewater.

In some cases it is possible to channel the wastewater out from the whole milk or whole milk substitutes shops and treat it in an anaerobic bioreactor to produce biogas with a methane content of 60 to 75%, which can be further used in the plant's heating system. A mandatory condition for the application of anaerobic treatment with methanation is a high COD load – with a concentration of more than 3000 mg/l. The general view of the anaerobic bioreactor is presented in Figure 2. Ecopolymer has experience in operating the processing highly concentrated wastewater treatment technology. Currently, Ecopolymer has designed anaerobic bioreactors for OST Group of Enterprises, city of Chernogolovka (Moscow region) [2] and Nadezhda CJSC (Krivoy Rog, Ukraine), and worked on the implementation of these projects.

General view of the anaerobic reactor

A complete treatment cycle is to supplement the local wastewater treatment plants with biological treatment and post-treatment facilities. The most modern areas in the implementation of the complete treatment cycle include nitri-denitrification with biological removal of phosphorus and membrane microfiltration. These methods are successfully used abroad, as well as in our practice of implementing wastewater treatment plant projects. The quality of water after such treatment meets the most stringent requirements for discharge into the fishery water bodies.

Subject to the fact that the local treatment scheme is most often used, Ecopolymer group of companies has accumulated considerable experience in the implementation of this technology. A number of projects were implemented, where Ecopolymer acted as the main contractor in the implementation of design documentation, equipment supply and commissioning.

Large industrial enterprises operate three shifts, therefore the coefficient of unevenness of wastewater supply ranges from 1.3 to 1.8. To smooth out the unevenness of the flow rate and wastewater pollution for physico-chemical treatment, as well as wastewater pH, equalization is used. This allows for stably high efficiency of wastewater treatment at the subsequent flotation and reduced amount of reagents introduced. The Western concept in the treatment of wastewater in the dairy industry is a large volume of equalization facilities: from 12 to 24 hours of wastewater handling. The general view of the flotation plant is shown in Figure 3.

General view of the flotation plant

The most significant advantage of the proposed wastewater local treatment plant is the fact that Ecopolymer flotation units show a very high efficiency of removing suspended solids, oils and fats, phosphates, and reducing COD and BOD.

No.	Parameter	Treatment efficiency, %	Food enterprise (on examples of implemented projects)
			No.1	No.2	No.3
1	Suspended solids	95 – 99	96.89 – 99.53	96.89 – 99.53	98.1
2	Fats and oils	93 – 99	93.23 – 99.51	93.23 – 99.51	85.4
3	COD	50 - 80	49.41 – 53.1	49.41 – 53.1	74.3
4	BOD5	50 - 80	52.81 – 71.76	52.81 – 71.76	77.4
5	Phosphates	70 – 95*	-	-	99.3*

No.

Parameter

 

Treatment efficiency, %

*Note: the efficiency of phosphate removal depends on the chemical composition of the water

As an example, we shall note the efficiency of a flotation plant for removal of fats, which design is described in the literature. It provides for 90-95% removal of fat, which is considered a high purification efficiency. In practice, with the proper selection of flotation equipment and reagents, it is possible to achieve greater treatment efficiency.

The high operating efficiency and reliability of the flotation units supplied by Ecopolymer GC is due to the peculiarities of their design. Flotation unit reservoirs are made of AISI 304 or AISI 316 stainless steel, the remaining structural elements are made of corrosion-resistant materials: polyethylene, polyvinyl chloride, etc.

The choice of design features of the flotation units is made at the stage of the study, where a particular type of the flotation units is selected from the existing five brands, as well as ancillary equipment: a recirculation pump and a compressor. Also, the study of the sewage system of an enterprise pays special attention to research on the effectiveness of induced air reagent flotation of wastewater. At the stage of laboratory studies, reagents and their doses are pre-selected: coagulant, flocculant and alkali, subject to the actual volume of wastewater and the availability of reagent suppliers near the object under study. Therefore, before the design begins, the customer already has reliable information about the scope of the operating costs and the expected quality of the treated wastewater. During the pre-design works, the wishes of the company's management about the level of automation, the expected timing of the installation and commissioning, the composition of the staff training program and the regulations of the treatment facilities, as well as the warranty period and the advantages of further maintenance are specified.

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