Waste management has become a major issue over the past decade, and as you can imagine, bio-digester vs septic tank is at the center of discussion.
With infectious diseases, pandemics, and epidemics erupting everywhere, not to mention global warming, people have to be cautious about how they dispose of and manage waste.
For the longest time, people have invested in septic tanks as their way of managing waste. But off-late, the idea of using a bio-digester has also become an option.
For many, they may not know what option to choose from seeing that they manage waste in a somewhat similar manner but they have different mechanisms and outputs.
Below we take a look at the differences between the two. Hopefully, by the end of this article, you’ll have your mind made up.
The Works of a Septic Tank
For every construction project, waste management is an essential part of the plan. They are always added to the building functions to allow a smooth architectural process.
Many even argue that when it comes to adding septic tanks, it’s much easier and cost-effective than using biodigesters. But before we look into that, let’s see how far back septic tanks go.
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History of Septic Tanks in Kenya
The first septic tank to be designed and constructed was back in the pre-colonial period of the years before independence. Back then, they were just small tanks that collect waste from the house, and once full, the exhausted came to empty.
Over the years, it became very common in use seeing people place them everywhere. From houses, rentals, office places, hospitals, and other areas.
Unfortunately because of its common nature, unqualified personnel went ahead to make their own tanks leading tonite failure and embrace of the new biodigesters.
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Sizing of Septic Tanks
Septic tanks are sized by the number of occupants they serve. For example, a two-bedroomed house, with four occupants will have an outflow of about 200 liters of water per day. This should have a septic tank of 1m wide by 1.5m long by 1.5 meters deep.
When septic tanks are constructed without the calculated dimensions, they will be too large, hence expensive to build.
Furthermore, the large size that is not commensurate with the number of users will make the internal conditions that aid the anaerobic decay not work effectively; leading to the tank getting full too fast or blocking altogether.
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Well, designed septic tanks will require grease traps at the entry point and exit point into the soak pit to prevent the grease from grey water; kitchen waste, clogging the soak pit pipes and preventing the soakage, which results in backflow buildup failure.
A grease trap costs Ksh 1,000 to construct, but when not put in place, it can result in frequent septic tank exhaustion costs or reconstructing the soak pit all over again.
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Septic tanks need an internal partitioning with the 1st chamber twice the size of the 2nd chamber, with the inlet into the second chamber located lower than half the height to prevent non-biodegradable waste from blocking the outlet.
A sufficient height versus surface area, tending towards deepness is better in ensuring the biodegrading of the waster into soak-able liquid onto the soak pit.
Well-placed vents at the last manholes will ensure that the foul smell will only be released very high up, ensuring the septic tank does not release any odor in the compound.
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The Works of a Bio-Digester
Now that we’ve seen the septic tank, let’s take a look at the Bio-Digester. We know that it works with a problem known as anaerobic digestion.
AD is the conversion of organic non-woody material (organic matter) in the absence of oxygen into stable and commercially useful compounds. AD feedstock can be biodegradable materials such as biomass, manure or sewage, municipal waste, or green waste.
The digestion process consists of four stages: hydrolysis, acidification, acetogenesis, and methanogenesis.
In the first phase, anaerobic bacteria use enzymes to decompose high molecular organic substances such as proteins, carbohydrates, cellulose, and fats into low molecular compounds.
During the second phase, acid-forming bacteria continue the decomposition process into organic acids, carbon dioxide, hydrogen sulfide, and ammonia.
Acid bacteria from acetate, carbon dioxide, and hydrogen during the acetogenesis phase. The final phase: methanogenesis, which involves methane-forming bacteria producing methane, carbon dioxide, and alkaline water.
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Use of Anaerobic Digestion
AD is widely used to treat wastewater sludge and organic waste because it provides volume and mass reduction of the input material.
Anaerobic digestion is widely used as its renewable energy source because the process produces methane and carbon dioxide-rich biogas suitable for energy production. Also, the nutrient-rich digestate or slurry can be used as fertilizer.
Outputs from the Digestion Process
After the long processes passing from chamber to chamber, we finally have the products and by-products. The outputs from the digestion process are:
This contains a mixture of methane, carbon dioxide, hydrogen sulfide, and traces of other ‘contaminant’ gases. This biogas is then combusted to generate heat, power, or road fuel.
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This is an inert and sterile wet product with valuable plant nutrients and organic waste. It’s a great source of organic fertilizer that can be used as manure for your farms.
The valuable component of Biogas is methane (CH4) which typically makes up 60 %, with the balance of carbon dioxide (CO2), and a small percentage of other gases.
The proportion of methane depends on the feedstock and the efficiency of the process, with the range for methane content being 40 % to 70 %. Biogas is saturated and contains hydrogen sulfide (H2S) which is partially responsible for the foul odor of flatulence.
In developing countries, the most common use of biogas is cooking. It gives a clean, smokeless blue flame. Where biogas replaces firewood as a fuel for cooking, this technology helps to reduce deforestation.
Also, as biogas burns much cleaner than traditional wood stoves, it helps to reduce eye and respiratory diseases caused by smoke in unventilated houses.
Besides, biogas can fuel an internal combustion gas engine in a Combined Heat and Power (CHP) unit to produce electricity and heat. The gas can also be upgraded and used in gas supply networks. The use of biogas in solid oxide fuel cells is, however, being researched.
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Only a small proportion of the total mass of the feedstock is converted into biogas. The solid by-product that is produced is rich in organics and nutrients, but almost odorless and partly disinfected, thanks to over 99% of pathogens destroyed in the process.
If you’d like to have complete pathogen destruction, then you would require thermophilic conditions.
The slurry is rich in various plant nutrients such as Nitrogen, phosphorus, and potash from potassium. Nutrients are conserved with more than 90% of nutrients entering anaerobic digesters conserved through the digestion process.
Well, fermented biogas slurry improves the physical, chemical, and biological properties of the soil resulting in qualitative as well as the quantitative yield of food crops.
Other uses of slurry include putting into ponds as feed for algae, water hyacinth, fish or ducks, and mushroom cultivation.
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In theory, any organic material can be decomposed anaerobically to produce biogas, but some materials work better than others. In general, materials need to be rich in energy and easily digestible.
Manure works very well, coming from cows, pigs, or horses. Bio-digesters can be fashioned from septic tanks, but the waste products are often not enough to produce enough biogas.
Plus cleaning agents from the greywater kill the anaerobic bacteria necessary for digestion. Plant material can be used, but acidic matter should be avoided, for they disturb the anaerobic processes.
The plant matter is also often low-energy and slow to digest, creating a number of difficulties for digesters relying solely on such material.
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The Science Behind The Biodigester Septic Tank
In some cases, you will find instead of having to choose between either choice, you can opt to have a bio-digester septic tank. Here’s how it works.
The sanitation system works through a process called Bacterial Biodegradation. This process completely breaks down organic matter or black water into gases and water. The gases produced are carbon dioxide, methane, and nitrogen.
It takes just about two weeks for the breakdown of matter to be complete, ensuring that only water is discharged out of the tank. This is made possible by the combined action of both aerobic and anaerobic bacteria present in the tank.
The bacteria are actually placed on the inside of the tank as it is being manufactured. The treated water can then be taken to a soaking area or other places where it can be recycled for other uses.
The carbon dioxide and the methane gas produced are simply released into the atmosphere while the nitrogen produced simply dissolves in the water.
This nitrogen-rich water is great for watering gardens and irrigation.
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Advantages of Bio-Digesters Over Septic Tanks
When it comes to sustainable green architecture in Kenya, many people are turned away by the cost. While the initial cost of installation for most solutions seems high, the long-term cost benefits and other benefits are amazing.
Here are some of the benefits of investing in this eco-friendly waste management system.
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Cost Friendly Installation
The biodigester septic tank is actually cheaper to install than the cost of constructing a traditional septic tank and the accompanying soak pit.
On the site, one needs to excavate a hole that is 1.1 meters deep and some trenches. The inspection chambers or manholes required are also few.
The system occupies much less space and can be used where space is an issue. Traditional septic tanks require a much deeper hole and that comes with high costs of excavation.
Excavation is also very tricky and expensive in areas that have a lot of rocks, swampy areas, or areas with high water tables as well as areas that have very loose soil.
Requires no Exhausting
Unlike traditional septic tanks, the biodigester does not need exhausting. This alone makes the biodigester the best option for dealing with sewer.
Exhausting a septic tank is the process of draining it when it is full. This process is undertaken after a number of years depending on the size of the septic tank.
The exhausting process is obviously an added expense, not to mention how messy and potentially hazardous it can be.
This on-site sewer system does not emit any smell whatsoever. Septic tanks emit a lot of bad smells because gases are released into the atmosphere. Imagine having to live with a foul smell that gets worse with every passing year.
Safe on the Environment
The biodigester enhances the environment in many ways, starting with the fact that it does not emit any smell. The water that is produced is usually soaked back into the ground and therefore increases the amount of water found underground.
The same water, which is rich in nitrogen and other nutrients can also be used for irrigation or watering gardens. This enhances the fertility of the soil.
Its byproduct, biogas has significantly reduced deforestation as people no longer need to cut down trees for firewood. This is why shipping container homes are using biodigesters since it supports their environmental safety standards.
Solid Structure and Design
The system is built out of reinforced concrete giving it structural strength that is superior to any other material such as cement, plastic, brick, or mortar. It can easily withstand pressure and stress making it extremely reliable.
The tank is small and cylindrical and thus, able to withstand pressure from the soil. This cylindrical design with a continuous wall ensures that stress is uniformly distributed, unlike rectangular designs where pressure is exerted on corners and joints.
The on-site sewer system comes with a 5-year post-installation warranty from the manufacturer which covers the manufacturer’s defects.
Approved by NEMA
The biodigester has been fully approved and recommended by both NEMA (National Environmental Management Authority) and the Ministry of Water and Irrigation for dealing with commercial and domestic wastewater in Kenya.
There’s no need to clearly state the leading system from the two, you have read about the major differences, read about the benefits, and even examined its works. You are now better informed.