What is Bacterial-Enzyme Digestion?
Bacterial-enzyme digestion is the process of bacteria consuming organic matter. The bacteria feed on the organic waste, deriving nutrition for growth and reproduction. The organic waste is metabolised down to water and carbon dioxide (the final metabolic waste products) providing the bacteria with energy to sustain their life. It may be simply shown by the following equation: Bacteria + Organic waste + Oxygen = Water + Carbon Dioxide
Bacterial digestant products must contain three necessary components:
• Bacteria • Enzymes • Essential Nutrients These three components work in harmony to digest organic waste speedily and efficiently with no odour or noxious gases.
Thousands of different types of bacteria exist everywhere in our world, and most of them carry on bacterial digestion in some way. However, some of them are found only in a particular environment and require specialised types of food, and/or have very unique biological roles. A bacterium is a single cell life form – each individual cell is a separate, unique organism. Bacteria often grow into colonies, jelly–like masses, but each cell remains an independent, individual life. Bacteria reproduce by a process called cell division. A mature bacterium reproduces by dividing into two daughter cells, each identical to each other and the parent bacteria. Under ideal conditions, bacteria can reproduce very rapidly, producing a new generation every 20 – 30 minutes. Following this reproduction process, the number of individual bacteria doubles with each generation. The population explodes as the number of organisms increases logarithmically. This population boom begins soon after the bacteria are introduced into a favourable environment, after a short lag time when the bacteria becomes acclimatised. This population cannot increase forever. At some point, the food source will be depleted, waste products will accumulate, or some other change in the environment will cause the population to level off or decrease (such as a change in pH, temperature, or oxygen level of the environment). Also, introduction of any poisons into the environment may have negative effects on the population, as well as competition from other types of bacteria. Bacteria can be classified into different types: • Aerobic types (which require oxygen to live) • Anaerobic (which can live without oxygen) • Faculative types can thrive under both aerobic and anaerobic conditions For waste digestion, several beneficial characteristics are crucial for the bacteria chosen for such products. The good bacteria used, must: • Digest waste quickly and completely, without producing significant odours or noxious gas • Consume (digest) a wide variety of organic material that are present in wastes • Grow and reproduce quickly and readily in the environmental conditions found in waste disposal systems • Not cause any disease in man or animals – they must be non-pathogenic Certain bacteria belonging to the Bacillus species have these desirable characteristics: • They consume organic waste thousands of times faster than the bacteria that are naturally present in waste. • They grow and reproduce easily • They are non-pathogenic, and do not produce foul odours or gas as they digest waste. These good bacteria are grown by artificial means on a liquid or dry nutrient medium. These cultured bacteria are then freeze-dried to put them in a state of suspension. They remain alive, ready to swim, eat and reproduce as soon as they are activated and put into the proper environment. The proper environment needed for a speedy growth and reproduction of these good bacteria must have the following characteristics: • Dissolved oxygen (for the aerobic types that require it) in sufficient quantities. • A water medium containing food (organic waste) for them to eat. • Moderate temperatures, between 10°C and 40°C. • Proper pH – not too acid, nor too alkaline – between 6 and 9 on the pH scale. Organic waste is consumed by the bacteria, used as nutrients by the bacteria and is no longer present to produce blocks, odours, slurry, pollution or unsightly mess.
What is an enzyme? How does it aid digestion? An enzyme is a catalyst that breaks up long, complex waste molecules into smaller pieces, which can then be digested directly by the bacteria. Enzymes are simply chemicals – they are not living things, and they cannot grow or reproduce themselves. Enzymes are manufactured by bacteria, and used by the bacteria in order to digest waste. The extra enzymes that are mixed into digestant products are actually produced by special bacteria, extracted from them in dry form and blended into the digestant mixture. Enzymes are added to digestants to enhance the efficiency of the digestive process. When added to the organic waste, the enzymes immediately go to work breaking down the waste. The large complex molecules of proteins, starches, carbohydrates and cellulose are broken into smaller, simpler pieces. These enzymes act like chemical blades chopping the large molecules of waste into smaller pieces of “prepared food” for the bacteria. The growing bacteria produce more enzymes on their own, creating a continuing cycle of enzyme production. The following four types of enzymes are often incorporated into digestant products: • Protease – breaks down proteins • Lipase – breaks down fats and greases • Cellulase – breaks down cellulose • Amylase – breaks down carbohydrates and starches Enzymes are specific, so that one type of enzyme can work on only one type of molecule. Thus, protease enzyme will break down complex proteins into simple pieces, but will have no effect on fats and greases. Likewise, lipase will attack animal fats and grease, but will not work on paper or wood fibres (cellulose).
Special nutrients are added to create the vitamins and minerals required for the fastest growth and the greatest activity of the bacteria. These vitamins and minerals may not be present in the waste, and a lack of any one of them may seriously inhibit the growth, reproduction and waste digestion performance. They must be added to the digestant product to assure the fastest, most efficient digestant action. The biological process of bacterial-enzyme digestion is responsible for the digestion of organic waste, no matter where it occurs. With minor variations, this same process digests waste in: • Drains • Plumbing • Municipal Sewer Treatment Operations • Septic Tanks • French Drains • Grease Traps • Cattle Waste Digesters • Chicken Manure Pits • Food Processing Waste • Ponds and Industrial Wastewater • Compost-Making • Organic Waste Disposal Systems
Case Study: The Bucket of Waste
You now have a basic understanding of the process of bacterial digestion. Lets follow the process when digestant is added to a hypothetical bucket of organic waste. Assume the bucket contains several litres of liquid, slurry of water with several kilos of cow manure. This waste bucket environment may be compared to conditions that exist in a septic tank or even a clogged drain. First, the digestant product is rehydrated with warm water, about 40°C. This warm water will reactivate the dead bacteria cultures, preparing them to go to work (hot water, above 70°C would kill the bacteria). At the same time the enzymes are dissolved and ready to begin the initial breakdown of the waste. When the slurry of digestant is added to the waste, the enzymes start working immediately, the protease begins to split the large protein molecules, and cellulose begins to break down grass and hay fibres. Cow manure contains no significant fat or grease, so lipase does little or no work. But if this was a grease trap… The reactivated bacteria have a short latent period to get acclimatised to the new environment, giving the starter enzymes time to produce many small fragments of food that can be immediately consumed by the bacteria. Under these favourable conditions, the bacteria soon begin to multiply, doubling their number every 20 – 30 minutes. This population explosion results in a tremendous number of bacteria living in the waste within a short time. The huge number of bacteria is able to digest large volumes of waste quickly. These bacteria were specially chosen for their ability to digest waste speedily and efficiently, without odours. Back to the bucket of waste… As digestion continues, the bucket of waste will change in appearance. The solid particles are liquefied, and the whole bucket will turn to a black liquid. As the process continues, the bucket will eventually clear up as all the organic matter is digested, with only a small amount of indigestible matter remaining. In real life, the process is a bit more complicated.
Closed Versus Open Systems
In this example, the bucket was a closed system. That is, nothing is taken out or added into the system other than what was there to start with. The consequences are important to consider, because this does occur in nature. A closed system tends to work against an efficient digestion process. Consider the following three occurrences: • The build-up of metabolic waste • The depletion of dissolved oxygen • Competition from other types of bacteria Because nothing is removed from the closed system, the end product of the digestion process (carbon dioxide) will build up in the system. This carbon dioxide is metabolic waste of bacteria. As carbon dioxide waste builds up in the water, it lowers the pH of the water (makes it more acidic). As more and more carbon dioxide is produced, the water becomes more acidic – and the environment becomes less and less ideal for the bacteria. In this closed system, the bacteria are poisoned by their own waste product (carbon dioxide), so the growth and reproduction rate are drastically reduced. In a similar manner, the available oxygen is used up. As the aerobic bacteria consume the dissolved oxygen, the environment becomes less conducive to growth and reproduction. Because more oxygen cannot be added into this closed system, the growth and reproduction rates decline even faster. (Note that anaerobic or faculative bacteria will continue digestion after the oxygen is gone!) Just like other living organisms, different types of bacteria compete for food and living space. In a particular environment, certain bacteria species may be more successful than others, and will eventually become dominant in that environment. For example, there may be hundreds of different types of bacteria naturally present in the cow manure in the bucket of waste. Some types of these naturally grow prolifically. As the conditions change, a particular type of natural bacteria may grow better than the ones that were artificially introduced with the digestant product. These competing bacteria may be more successful and overpower desirable bacteria. However, these successful bacteria may not digest the waste as well, or produce foul odours, or even be pathogenic. These and other possible changes in the environment may drastically slow the process of digestion. It may take many times longer to digest the 20% of the waste as it did to digest the first 80%.
Continuous Digestion: The Open System
A closed environment poses potential problems with the process of bacterial digestion. Fortunately, most real waste systems are open systems. With an open system, things can be added and removed to maintain the environment in a condition that is most favourable to the growth of beneficial bacteria. Consider the bucket of waste: • The pH of the water may be adjusted to maintain conditions that promote the growth of the desirable bacteria. As the carbon dioxide builds up, a small amount of caustic soda or another alkaline chemical can be added to adjust the pH within the best range. • The bucket can be stirred or otherwise aerated to replenish the dissolved oxygen supply. The added oxygen will encourage continued bacterial growth and rapid digestion, because the most favourable growing conditions for the beneficial bacteria are maintained. • Additional doses of digestant can be added to aid the population of the desirable bacteria. This is done to insure that the good bacteria will remain plentiful in the face of tough competition from all the naturally occurring bacteria. These techniques are often used in large sewer treatment plants. By actively working to maintain a healthy environment, the growth of the desirable bacteria can be maximized. The conditions may be monitored and adjusted to keep the process of bacteria digestion going on full speed, with an absolute minimum of gas or odours, and resulting in the fastest most complete digestion of the organic waste. This introduction is designed to help you understand some of the principles involved in bacteria digestion. While the process is the same for almost all waste systems, the actual conditions will vary greatly from system to system. Each type of system will have its unique problems to be overcome. By understanding the way digestants work, and what makes them work best, you can fine tune the treatment programme to produce the best results – while minimizing the cost of the treatment.
Municipal Sewer Treatment Plants
Most municipal sewer treatment plants use bacterial digestion to treat waste water. There are many methods and devices used to do this, but they all use bacterial digestion to remove organic waste from waste water. Raw sewerage coming into treatment plants contain: • Grit – stones, coffee grounds, plastic and cloth, sand, cigarette butts, and other non-biodegradable matter • Suspended Solids – particles of organic waste that are able to be settled out of the water • Dissolved Solids – particles of organic waste that are very fine and soluble and cannot be settled out of the liquid • Water The job of the treatment plants are to remove as much of the grit, suspended and dissolved solids as possible. When these are removed, the clean-up water is discharged into a lake, river, and sea or allowed to trickle down into the ground. Biological Oxygen Demand (BOD) is an indirect measurement of the amount of organic matter in the water. This test shows how much oxygen bacteria would require if they were to digest all the organic material in the water. This test is based on the fundamental chemical reaction that describes bacterial digestion: Bacteria + Organic waste + Oxygen = Water + Carbon Dioxide BOD is expressed in parts per million, or ppm. When the BOD of water is high, it means that the water has a lot of organic matter in it – and that bacteria would demand – or use – a lot of oxygen to digest that amount of organic material. Likewise, a low BOD measurement shows that most or all of the organic material has been removed from the water.
The Treatment Process
As raw sewerage effluent enters the treatment plants, the first step is to filter out any sand, grit, stones, cigarette butts and other hard, insoluble matter. Mechanical filters, screen assemblies and settling basins, do this. The next step in the process is to separate the suspended organic solids from the water. This is done in a device called a primary clarifier. In this clarifier the suspended solids are settled to the bottom, sometimes with the aid of flocculating agents. After settling out as much of the suspended solids as possible, these solids are pumped out of the bottom of the primary clarifier as sludge. This process removes most of the organic waste from the water. However, the liquid portion that remains behind is clean yet. The liquid contains all the dissolved solids, and further processing of this liquid is required. After this point, the sludge and the liquid portions of the waste are treated separately. The remaining liquid contains dissolved organic matter that must be removed by bacterial digestion before the water can be regarded as clean. This is done in another device, usually called the oxidation tank. This device is easy to identify by its bubbling and gurgling action, caused by air being forced through it (aeration). This aeration promotes the bacterial digestion process, and within several hours, the bacteria will digest most of the remaining dissolved solids. When the digestion is complete, the liquid waste then goes into a final clarifier or finishing pond. Here, the liquid is held motionless and any remaining solids (including the bacteria) are settled to the bottom. It is then pumped out and treated with the sludge. The remaining liquid will be almost clear, as most of the organic matter has been removed from it. Often the water receives one final treatment before it is discharged to a lake, stream, sea etc. The final treatment is disinfection and it kills all the bacteria that might remain in the water. This is required to prevent any pathogenic organisms from being discharged into the environment. The sludge that was separated out of the primary clarifier is pumped to a digester where it is also treated by bacterial action. This slurry must eventually be disposed of by some method, such as land filling, incineration, sea disposal or application to farmlands as fertiliser. The purpose of treating the sludge is to: • Reduce the weight and volume of the sludge • Transform the sludge into a liquid or solid cake form that can be processed, handled, transported and disposed of easily and economically • Reduce any odours as much as possible • Kill all pathogenic organisms before slurry is returned to the environment Processing of the slurry is designed to accomplish these goals at the lowest possible cost. Thus, the slurry treatment process used in a particular treatment facility will vary according to how the slurry will finally be disposed of. For example, if the slurry will be incinerated in a high temperature furnace, the main objective of slurry treatment will be to reduce the water content, so it burns better. The actual incineration will take care of the other concerns. Most slurry is disposed of by returning it to the environment, that is, the treated slurry is applied to farm fields as fertiliser. When this is done the slurry must be treated carefully, so that it does not pose a pollution threat or other environmental threat to people, animals, crops or ground water. Digesters have proven to be the best treatment process to prepare municipal sewerage slurry for land application. Digestion produces treated slurry that is perfectly suited to land disposal, due to bacterial digestion. A digester system can be designed for either aerobic or anaerobic operation. In either case, it is very important the bacteria are of the correct type. If not, neither system will be effective. The incorrect type of bacteria is one the most common causes of digester failure. An aerobic digester may be functioning well for a long time. Then, within the space of a few days, the operator might notice drastic changes occurring. The temperature in the digester drops, the slurry takes on an unusual appearance and the normal bubbling and churning slows – then stops completely. In such a case the digester has gone septic and is not functioning at all. No bacterial digestion is active to break down the slurry. This type of failure can have several causes, such as wastewaters that contain toxic heavy metals, pesticides or petroleum. But the most common cause is simply a lack of the correct types of bacteria. The digester stops working because there are not enough good waste-digesting bacteria in it. Instead, other naturally occurring organisms have taken over, displacing the desirable bacteria. The only way to fix this situation is to kill all bacteria present, then re-seed with a digestant product that contains the right kinds of waste digesting bacteria. This is done with a very powerful disinfectant chemical called hydrogen peroxide. The process of restarting a digester is laborious, time consuming, expensive and involves the handling of very hazardous chemicals. It may take days to accomplish holding up all other operations, and the treatment plant will not be able to treat the influent waste water. The best way to keep a digester working smoothly, efficiently and without disruption is to add daily or weekly doses of a good digestant product. This will ensure that there are always enough of the good waste digesting bacteria present to prevent any disruption of the digester. In addition, the especially cultured bacteria and enzymes in a digestant will make the whole treatment process work better. Digestants should be added to the digesters, oxidation tanks, trickling filters and settling tanks: • Bacterial oxidation of the liquid will be faster and more complete • Digesters will operate evenly and uniformly, resulting in easier planning and routing of waste. • Slurry volume will be reduced more, as more solids are digested • Slurry will be easier to pump, process and dewater, and have fewer odours • The capacity of the system will be effectively increased, because more waste can be processed, more completely, in less time • The whole system will be better able to absorb the shock of toxic influent • Effluent water quality standards will be met more consistently, helping to maintain a clean environment and safe drinking water for the whole population • Drain and septic system maintenance
Blocked plumbing can cause a disaster…Operators of commercial kitchens, schools, and institutional cafeterias, restaurants, bakeries, and butcher shops have a very real concern about the maintenance of their drains and grease traps. Blocked plumbing can cause flooding, contaminated food, cause and jeopardize the sanitary condition of an entire facility. Many Rands and hours of hard work must go into cleaning, sanitising and restoring the facility. Preventative maintenance with a digestant treatment programme can greatly reduce the risk of such a disaster. The aim of a digestant treatment programme is to reduce the frequency of clogs and grease trap pump out. At the same time the programme will provide better results at less cost than the local plumber or grease trap service. A few Rands worth of bioenzyme digestant used properly can save many Rands worth of aggravation, inconvenience and service calls.
Drain and Sewer Blockages
Any drain, sink or toilet will become blocked if a roll of paper towelling is stuffed into it. But this is not a normal occurrence! Things that should not clog drains, like a clump of cold mashed potatoes or meat trimmings, cause drain blockages. When a sewer pipe is new, it has an inside opening the full diameter of the pipe (10 – 15 cm for many sewer lateral pipes). Over time, bits of food and grease cling to the walls of the pipe. As this normal accumulation builds up, it slowly closes up the pipes. Eventually, enough accumulation will build up to reduce the effective pipe size to a fraction of what it should be. A 10 cm pipe will easily handle a clump of mashed potatoes, but when it has been closed up to only 5 cm, the potatoes can cause a blockage. Thus, keeping the sewer pipe at its maximum diameter can prevent most blocks. To achieve this, one needs to introduce the bacterial digestant into the pipe. The bacteria will become established within the accumulation on the walls of the pipe. Bacteria will grow and reproduce in this layer of organic matter, while continuously carrying on the normal digestion process. However, they will never clean it down to the bare metal or plastic, and that there will always be a thin layer of organic accumulation on the walls of the pipe. The bacteria will continue to live and grow in this layer, and they will always be present to continuously digest organic matter that might cling to the walls of the pipe – eliminating the cause of most blockages.
Treatment Of Drains and Sewer Lines
A drain treatment programme is quite simple, but must be followed precisely for best results. This treatment must be done at least weekly. Treat just before the kitchen will be closed for the longest possible time. For instance, if the kitchen will be closed all weekend, the digestant should be added at closing time on Friday night. If a facility does not close for more than a few hours, or never closes completely, add digestant when the water flow will be lowest for several hours. A peristaltic automatic dosing system is ideally the best way of treatment. The specific amount of digestant to be used depends on the size and type of drain. Drains that receive heavy loading of organic material (dishwasher drains, waste disposal, floor drains etc.) should get more aggressive treatment. Also treat drains that have a history of blockages with higher dosages of digestants.
Septic Tanks And French Drains (with Drains Fields)
A septic tank is a very simple and small sewer treatment plant. It contains baffles that are arranged so that all small matter falls to the bottom of the tank. This solid matter is held in the tank where bacterial digestion will break it down. There must be sufficient numbers of beneficial bacteria in order for this digestion process to take place. Many chemicals (strong cleaners, drain openers, and bleach) will kill bacteria and the digestion process is interrupted. A digestant product should be added to the system regularly to keep the entire process working properly. Liquid waste flows out of the tank and into the drain field. In the drain field soil and bacteria work to purify the liquid waste as it percolates into the ground. If the septic tank is not functioning properly, solids may be washed out of the tank into the drain field. Here they block the pores of the drain field. The drain field has been specially constructed of sand and fine gravel to allow the effluent from the septic tank to filter slowly into the ground. If the pores of the drain field are blocked up with solids, the liquid effluent will not filter properly, creating piddles of standing wastewater and causing the whole system to block up.
Treatment of Septic Tanks and French Drains
Septic systems should be treated regularly to ensure that there is a good supply of beneficial bacteria in the septic tank. Choose the amount of treatment based on the size of the facility and the usage of the system. Add the treatment through a toilet that is nearest to the tank. A heavy initial dose (double or triple the normal amount) will help to get the system functioning quickly. Then cut back to normal monthly amount, and treat on a regular schedule. If the system is used heavily or problems are noted, treat the system weekly. Like all the other systems, it should be treated 24 – 48 hours after the use of any strong disinfectants or drain openers. This will replace any bacteria that may have been killed by the chemicals.