Lesson 4 - Effluent Treatment

Effluent treatment and management are important in order for us to dispose of the liquid waste generated by the brewing process.

Effluent is defined as the liquid waste flowing from a process.

For the purposes of this lesson, we will focus on effluent treatment and not the sources of effluent. First, let us quickly look at the typical sources of effluent in a brewery:

• Effluent from cleaning equipment, containers, and buildings (including spent detergents and rinse water)

• Effluent from process, such as wort, beer, trub, and yeast

• Effluent from services and utilities, including water from pasteurisers, cooling water, and boiler blowdowns

Depending on the source, the quality of the effluent can vary with respect to a number of parameters:

• Concentration (strength), which is a measure of how diluted or concentrated effluent is

• Solid content (e.g. high levels of spent grains, spent yeast, or filter materials such as kieselguhr – we do not want this in our effluent)

• pH (e.g. if caustic, acid, wort, or beer gets sent to drain – something we want to avoid)

• Chemical composition (chemicals can enter the effluent via raw materials, processing aids, and cleaning processes)

  • This can include heavy metals and other components which may not be allowed in the effluent depending on your effluent discharge regulations

• Contaminants (e.g. oil and grease)

• Temperature (e.g. hot water vessel rinses)

Untreated brewery effluent parameters

We will only review these briefly, as you should be familiar with them from previous studies or experience.

Let us quickly recap the definitions of a few of these parameters.

Total suspended solids (TSS) is the amount of suspended particulate matter.

The chemical oxygen demand (COD) measures the theoretical amount of oxygen required to break down biological matter to a level that is acceptable for discharge. COD can be measured several ways. A common test is to use a mixture of sulphuric acid and potassium dichromate to provide the oxygen. The potassium dichromate is used up in the process as it oxidises organic matter, so measuring the amount of potassium dichromate left after the test tells us how much oxygen is required. 

The biological oxygen demand (BOD) measures the amount of oxygen required by micro-organisms to digest the most readily available nutrients present in the effluent. The amount of oxygen consumed is measured over a five-day period. The test is thus known as BOD 5. This value is usually lower than the COD, and the difference indicates the ease/difficulty of digestion.

The BOD, COD, and TSS are known collectively as the effluent loading. This is basically how dirty the water is or how much treatment it will need before it can be safely discharged to a watercourse.

The table below shows the most important untreated effluent parameters.

Table: Typical brewery effluent parameters

As you can see, these cover a wide range of values. They vary from brewery to brewery, and within a brewery on a seasonal, daily, or even hourly basis.

Cost-effective effluent treatment starts with well-designed and well-run brewing and packaging processes.   

Effluent discharge parameters

Effluent discharge from a brewery is subject to legislation in terms of what and how much is allowed. In many cases, a brewery must adhere to agreements made with local authorities which can take the form of ‘consents’ or ‘discharge permits’. If discharging to sewer, effluent consents will specify the aspects of effluent discharge that have the potential to cause the municipal treatment works problems. If effluent is to discharge to a watercourse the consent will specify elements which have the potential to harm aquatic life. In both cases limits are typically imposed on the following:

• Daily volume

• Instantaneous flow

• pH

• Loading (COD, BOD and TSS)

• Temperature

• Heavy metals

Effluent charges are calculated on the basis of the volume and the loading of the effluent. To understand how the fee is calculated, we will use the system used in the UK as an example. This is known as the Mogden formula:

P = C + V + (St / Ss) S + (Ot / Os) O

Where:

P = cost per m³

C = conveyance charge per m³

V = volume charge per m³

S = suspended solids per m³

O = COD charge per m³

St = suspended solids content of trade waste (your waste) in mg/L

Ss = suspended solids content of sewage (of the current waste at the treatment works) in mg/L

Ot = COD of trade waste in mg/L

Os = COD of sewage in mg/L

Effluent treatment overview

Effluent treatment can range across:

• Virtually nothing (e.g. if your municipal treatment is inexpensive and can handle your volumes, or if you are a small operation)

• Basic (to meet your effluent discharge specifications according to your consent to discharge or permit or other regulations)

• Intermediate (to save on effluent costs)

• Advanced (for water reuse)

Effluent treatment covers a wide range of technologies. The choice of technology depends on many factors.

Effluent treatment is normally divided into three phases:

• Primary treatment (pre-treatment) can either be to prepare the effluent for further treatment or to treat it sufficiently to meet the minimum discharge requirements (although this is not very common). It normally focuses on removing solids from the effluent and bringing the pH to the right level.

• Secondary treatment (main treatment) focuses on reducing the total biological and chemical load in the effluent to meet more stringent discharge requirements.

• Tertiary treatment (polishing treatment) focuses on treating the effluent to allow for reuse in the process.

Effluent treatment processes can be physical, chemical, or biological.

We will now describe each of these effluent treatment phases in more detail.