Module 5. Building construction materials and type of building construction

Lesson 30


30.1 Introduction

The ratio of milk to water used in various dairy plants varies from 1:1 to 1:3 depending on the type of plant. The old figure of water use was quite large but now water conservation measures resulted in to considerable low level of water consumption. Water is mainly used for washing of equipments, floors, milk crates/cans, hot water, chilled water etc. When water is used in dairy plants, it is necessary to provide drains and piping arrangement to transfer the waste water to effluent treatment plant (ETP) of the dairy. The drains and pipeline layout should be such that it maintains hygienic conditions in the processing area and waste water containing milk resides is efficiently collected from all the sections and finally supplied to the ETP plant.

30.2 Drainage System for Dairy Plants

Drainage system is very important in dairy plant. Therefore, it is one of the essential considerations at the stage of planning and design of dairy building. It is important to provide adequate numbers of sanitary drains coupled with waste water conveying system to transfer the effluent to the treatment plant. Any shortcomings may lead to choking of drainage pipelines and unhygienic conditions in the plant. Cast iron or PVC pipelines are commonly used for conveying of effluent in dairy plants. The planning and lay out of the drainage system is done in such a way that it is possible to separate high BOD and low BOD effluent. This is necessary to adopt different methods for the treatment of effluent. Anaerobic method of treatment of high BOD effluent is getting considerable importance in dairy industry as its operating cost is low and it generates methane gas which can be used for boilers. The following points should be considered while planning and laying of drainage system.

1. Select the most appropriate type of drains and entire system considering hygienic conditions.

2. Use the drains which can be cleaned easily.

3. Provide adequate number of drains considering the maximum flow of water.

4. Use of 4”-5” (100 mm to 125 mm) diameter pipe for drainage lines for handling milk plant wastes.

5. Regular cleaning of sanitary drains is recommended to avoid chocking of drainage system.

30.3 Floor Traps for Dairy Floors

A trap is a device which is used to prevent sewer gases from entering the processing area of the building. The traps are located below or within a plumbing fixture and retains small amount of water. The retaining water creates a water seal which stops foul gases going back to the processing area of the building from drain pipes. A good trap should maintain an efficient water seal under all conditions of flow. In Gujarat, sanitary trap used in large capacity dairy plant are popularly known as Amul trap (drain) which is fabricated using 2 mm thick stainless steel and is available with the sanitary design for dairy and food industry. These are available in various specifications and finish based on the need of industry.

Drains for dairy plant floor may be square type or round type. A trap is placed beyond or underneath the drain. A typical floor trap is given in Fig. 30.1 which has two cast iron cover plates, the lower one perforated and the upper one slotted. The top plate retains big size materials such as bottle caps, threads, glass pieces etc. while lower perforated plate retains relatively smaller size materials. The debris retained on these plates can be removed.


Fig. 30.1 Floor trap with cover plates

30.4 Design Consideration for Drainage System of Dairy Plant

The efficient collection of the effluent from all the sections of dairy plant and conveying of the effluent are two important considerations for the drainage system of dairy plant. There are two categories of drainage system.

1. Drainage system for different sections of dairy, laboratories,

2. Storm water drainage system for collection of rain water from roof, surface water from paved areas. This water is quite clean and can be handled for useful applications such as water re-charging of wells/tube wells. The system consists of big size cannels and cement pipelines of big diameter, pumping etc. This system of rain water management is also very important in order to eliminate water accumulation in the dairy premises.

In this lesson the main emphasis is given for the drainage system for different sections of dairy plant. This system is continuously in use throughout the year and hence adequate attention is required to design and laying of the system. Some of the important points to be considered are indicated below.

Floor in the processing section should be laid with adequate fall so that water runs quickly to drain. This is also important to extend the life of the floor. The minimum slope should be 1:80 and slope up to 1:40 is considered better from point of view of drainage. The recommended slopes in floor towards drain for processing room is 0.25 inch per foot and 1/8th inch per foot for cold store. The probable places where spillage of milk may occur. The slope should be arranged in such a manner that liquids will flow to the drain by the shortest route.
• The arrangement of drains in a large processing room is shown in Fig. 30.2. In this layout, the entire floor of the large milk processing unit is divided into 8 segments and 8 floor traps have been placed to catch liquid flow from the floor segments. Liquid falling on any of the segments will quickly move towards nearest trap. Drains underneath the traps run in straight lines as shown in Fig.30.2 and meet the main drain line which later joins the main sever line. This type of layout is highly recommended for large milk processing rooms. For small processing rooms, this type of arrangement may be provided on the side of the wall keeping about 30-40 cm distance from the wall.

Use vitrified salt glazed clay/concrete/PVC sever pipeline to transfer the dairy effluent to treatment plant.


Fig. 30.2 Drain layout of a large milk processing room

Last modified: Thursday, 25 October 2012, 6:41 AM