Commercial bakery wastewater treatment
Commercial bakeries produce a strong type of sewage that poses a risk to the environment without the right form of wastewater treatment. Even if discharging to a mains sewer, raw bakery sewage is still much too concentrated for a municipal treatment plant to process.
Although nontoxic, bakery wastewater is high in organic compounds which are harmful to ecosystems if not sufficiently broken down. As a result of washing and rinsing equipment and floors, over half of the water a bakery uses ends up as sewage. This type of sewage is oxygen deficient and high in organic compounds due conditions that hinder the biological breakdown process such as;
- the lack of particular nutrients to feed the bacteria responsible for breaking down organic matter
- the presence of oil and grease that deprive the bacteria of the oxygen they need
- the use of excess cleaning agents that inhibit the growth of bacteria to large enough numbers
When raw sewage like this enters the environment it wreaks havoc with the natural ecosystems and as such, wastewater treatment is absolutely essential for a commercial bakery.
Discharge limits for commercial bakeries
Whether a bakery discharges to a public sewer or has its own treatment plant on site, there are strict discharge limits in place to protect the environment. Local governing bodies will issue a commercial bakery with a discharge license provided that it can meet the specified discharge limits. For example, details for consent to discharge to the Anglian Water region can be found here.
There will be regular inspections to check that the wastewater continues to meet the requirements set out in the license. It is the responsibility of the bakery owner to ensure compliance with the license or otherwise risk hefty fines and even closure of the premises until the necessary action has been taken. You will find information about the Irish legislation by following the link below.
Under Section 16 of the Local Government (Water Pollution) Act 1977 (as amended), an individual or business may not discharge a trade effluent to the sewer except in accordance with a licence issued under these regulations.
Meeting discharge limits will require the services of a reputable wastewater treatment company who can plan and implement a solution for treating the bakery wastewater to the correct standards. They will design and provide a suitable onsite wastewater treatment system to meet the demands of the bakery and the local discharge limits.
Bakery wastewater treatment systems and processes
In general bakery wastewater contains high contents of organic pollutants, suspended solids (SS) and fats, oils and greases (FOG) which result in a high chemical oxygen demand (COD). Whether discharging direct or to a municipal plant, effectively treating wastewater with high COD requires a series of physical, chemical and biological treatment processes.
The main organic components in bakery wastewater are flour, sugar, oil, grease, and yeast. Primary treatment of bakery wastewater involves reducing the suspended solids and removing the floatable FOG. Secondary treatment involves removing the dissolved biodegradable components through a biological process using microorganisms/bacteria.
The volume and strength of the wastewater depends on the products/processes and varies according to the operational times of the bakery. For example, pastry produces the greatest volume of wastewater while cakes produce the strongest wastewater. Because the flow rate and loading of bakery wastewater will vary throughout the day, an equalization tank or buffer tank for temporary storage can help to meet the demands of peak discharge times.
Primary treatment requires a screening process to firstly remove any coarse particles in the bakery sewage. Screens vary in the size of the openings from micrometers to in excess of 100 millimeters. The right type of screen will depend on the characteristics of the wastewater and the requirements of the bakery. The next step in the treatment process involves separating and skimming FOG from the screened wastewater. Traditional treatment systems use mechanical scrapers to remove FOG from bakery wastewater. Acidification can further help to break down any remaining FOG by adding an acid such as sulfuric acid which helps to keep the pH at an optimal level. Coagulation and flocculation work on any remaining fine SS by making the particles clump together for easier removal with the addition of chemicals such as alum and ferric chloride combined with a mixing process.
DAF for primary treatment of bakery wastewater
Dissolved air flotation (DAF) is an effective, proven means of bakery wastewater treatment. A good DAF system will remove SS, FOG, control pH and precondition the wastewater to a level optimum for secondary or biological treatment. For a commercial bakery discharging to a public sewer, a DAF system is an ideal solution to improving the quality of the wastewater so that it meets discharge limits and is safe for treatment at a municipal plant. If a bakery is not discharging to municipal sewerage works, the wastewater will require secondary treatment prior to discharge.
Biological treatment of bakery wastewater
The objective of secondary or biological treatment of bakery wastewater is to remove the remaining biodegradable components in the wastewater using microorganisms. There are different methods to achieve this but the most suitable one will depend on the requirements of the bakery. A wastewater professional will be able to make recommendations or carry out tests to determine which method will work best.
The most common form of secondary treatment for bakery wastewater is the activated sludge process which uses suspended growth microorganisms. Here, waste flows around and through free-floating microorganisms and settles out as a type of sludge, most of which can be recycled back into the system. The typical arrangement of an activated sludge process is an aeration tank (bioreactor) that provides the bacteria in the wastewater with oxygen, and a settling tank (final clarifier) to allow the resulting sludge to settle and be reused/removed.
SBR for secondary treatment of bakery wastewater
A sequential batch reactor (SBR) is very effective biological treatment system that uses the activated sludge process. An SBR system treats batches of wastewater in a timed sequence. While the final clarifier is settling and decanting, the bioreactor is aerating and filling. Clear water collects in the top of the clarifier where it is now clean and suitable for discharge. SBR is just one method of biologically treating wastewater from a bakery, there are many others. Again, the most suitable system will depend on the size of the bakery and the characteristics of the wastewater.
In the end, the most important thing to realize is that without a treatment system, bakery wastewater is harmful to the environment. It could potentially be harmful to the business too if discharging it without a license or failing to meet the conditions of an existing license. Installing a treatment plant in a bakery doesn’t have to be a monumental task, a reliable wastewater treatment company will help to come up with a solution that meets the requirements of both the bakery and the discharge consent.