Lesson 2 - Brewing Water Sources and Treatment
This lesson introduces water as an ingredient for brewing. It explores the water cycle, sources of water and potability standards. It also examines some characteristics of water (hardness and alkalinity) and their effects on the brewhouse. Finally, the lesson investigates the methods of water analysis.
Raw Water Treatment
The specific steps taken to purify water to meet potability standards will vary depending on the source of raw water. This section covers the main principles of achieving potable water, as well as exploring what a typical potable water standard is.
Abstraction
Water is either sourced from surface water (usually less clean than groundwater) or groundwater. This is termed ‘raw water’, and is either pumped into a large, open storage reservoir temporarily, or is pumped directly into the treatment plant.
Storage reservoirs can be seen as an initial treatment step as they blend water from different sources, which can dilute some incoming contaminants from a particular water source. A long storage time in these reservoirs allows some of the solid contaminants to settle to the bottom; sunlight begins to break down the organic material.
Screening
Screening involves filtering the water (from reservoirs or directly from surface or groundwater) through metal grills and screens to remove solid objects. Coarse screens help remove large objects such as weeds, leaves, sticks and other debris. Fine mesh screens will remove smaller particles, such as small fish and large clumps of algae.
The next series of steps may take place in a different order; some may not be used at all, depending on the levels of contamination in the screened water.
Clarification (Coagulation and Sedimentation)
The screened water is dosed with a chemical coagulant, which helps fine suspended material (such as silt and mud particles) to bind together. As these coagulated particles clump together, they form a ‘floc’ (precipitate), which then either settles to the bottom or floats to the top using flotation. Flotation is a method in which micro air bubbles attach to the flocs, causing them to float, where they are then removed. Larger particles settle/rise faster than fine particles, so coagulation ensures that larger particles are formed from fine particles. The chemical coagulants may be aluminium sulphate [Al2(SO4)3], ferric chloride (FeCl3), ferric sulphate [Fe2(SO4)3] or polymer additions.
Coagulation reduces the time required to settle out suspended solids ‒ especially smaller particles including bacteria, viruses and protozoa.
Sedimentation may occur in separate tanks that are rectangular (length to width ratio of 2:1 to 5:1) and a depth of 1.5-2 m. The inlet and outlet are at opposite ends, with the flow designed to ensure that water is spread evenly, and passes through slowly, to allow maximum sedimentation.
Filtration
There are a number of different filters available, but they all have the same purpose – to remove suspended material from the water.
Sand filters act as a microfiltration system, which removes turbidity, algae and micro-organisms. As water flows through the sand bed, the top layer traps organic material and micro-organisms. The organic material then helps support the growth of bacteria and the trapped micro-organisms, which then breakdown dissolved organic compounds in the water as it trickles through the sand bed. This provides additional cleaning action.
There may be multiple filtration steps throughout the whole process.
Aeration
Aeration, by air stripping, removes volatile organics, carbon dioxide (CO2) and some taste and odorous compounds (such as hydrogen sulphide ‒ H2S).
Aeration also oxidises some metals such as iron (Fe2+) into the insoluble ferric hydroxide [Fe(OH)3], which is precipitated out and removed by filtration.
Granular activated carbon
Water is directed into vessels that contain granular activated carbon (GAC), which is porous and able to adsorb organic compounds from the water.
The carbon can become saturated, and will thus need to be regenerated. The GAC is backwashed with water and then steam is used to regenerate the GAC. This enables the GAC to effectively remove organic compounds again.
pH adjustment
We may need to adjust the pH value to meet water quality standards. This also avoids any corrosion or scaling of the municipality and brewery pipelines.
The coagulation process tends to make the water more acidic but removing carbon dioxide by aeration can help increase the pH. To adjust the pH, various chemicals can be used. To lower the pH, acids such as sulphuric (H2SO4) or hydrochloric acid (HCl) are commonly used. If the pH is too low, then alkaline chemicals, such as sodium hydroxide (NaOH) or sodium carbonate (Na2CO3) can be used to raise it.