Dome of Bio-Digester in Kenya under construction

Digester Wastewater Treatment

Wastewater is known to cause numerous problems and illnesses that it cannot be substantiated, hence the need for wastewater treatment. And while people have been accustomed to using septic tanks as a way to manage waste, here’s a way that is known to do it the right way. Protecting people’s health as well as the environment.

So, in this article, you will read about how the digester is taking the lead with waste and wastewater management. How people are even benefiting from this kind of treatment system. By the time you’re done reading, you might even be convinced to buy and install it in your next shipping container home project.

The Principle of Wastewater Treatment

Dome of Bio-Digester in Kenya under construction
Bio-digester for wasterwater treatment

Biodigesters as a waste management system had been known to provide 100% recycling capabilities. It treats waste in both an aerobic and anaerobic way, similar to nature, except in this case the process is hastened. All the waste from toilets, bathrooms, kitchen, and sinks can be transformed significantly into something worthwhile for use at home and on your farms.

Because the waste is organic, the bacteria present in the chambers biodegrade the organic matter, while recycling the water for use as irrigation for your agricultural purposes.

To better understand the principles of wastewater treatment, let’s first take a look at the parts of the bio-digester and the role each one plays in terms of treating and managing waste.

  • A bio-digester tank – the tanks are designed to act as incubators to bacteria and to provide all the conditions necessary for the aerobic and anaerobic decomposition of organic waste. An enzyme can be put into the tank to catalyze the process.
  • A gulley trap – this is designed to capture solid particles in the wastewater. This protects the bio-digester from filling up.
  • A grease trap – So, this uses the property of an oil to float on the water and its viscosity to separate it from the water. Oil should be removed from the wastewater before treatment. This allows for easy aeration of water for bacterial action.
  • Recycling tanks, pumps, and irrigation systems – after the waste has been treated, clean water free from pathogens will be released in the process. The pumps and irrigation systems play a vital role in collecting this water.

As you can see, every part of the biodigester plays a vital role in the treatment plan. For you to realize the products as well as the benefits, every section has to perform its role efficiently.

The Process of Anaerobic Digestion as a Wastewater Treatment Plant

There are different ways to treat and manage waste, but with biodigesters, the main aim of treating the waste besides reducing the sludge is to come up with eco-friendly ways to deal with the waste. That is why anaerobic digestion is one of the most employed methods for this process.

A large fraction of the organic matter is broken down into carbon dioxide (CO2) and methane (CH4), without the presence of oxygen. About half to 60% of the amount is then converted into gases, while the remainder is dried and becomes a residual soil-like material.

To be able to do that, the biodigester had to be constructed in such a way that three factors don’t interfere with the digestion. These are;

  • No presence of oxygen – once oxygen is produced, the matter will then be oxidized forcing the matter to just simply decompose without forming the extra percentage of gases known as biogas.
  • Escape of odor – one of the best features of a biodigester is the inability to smell the awful pungent smells emitted by the waste.
  • Availability of the gasholder – without a gas holder, the air can’t be captured rendering the biogas plant useless. 

So in order to get the proper effluents from the process — methane and organic fertilizer — all these elements have to come to play. Otherwise, the process will turn aerobic and function like a septic tank that needs constant maintenance and exhaustion. Begging the question, did you really treat the waste or just managed it?

Treatment Steps

So, what wastewater treatment is undertaken for the waste to be efficiently dealt with? You will find out that there are numerous processes under which anaerobic digestion occurs. To spare you all the scientific and chemical terms here’s just a lay description of what happens in the digester while it goes through all its three chambers.

● First off, all incoming flows of sludge (grey matter, animal waste, black matter) are combined. Then the mixture is heated to a mild temperature to accelerate biological conversion, sometimes an enzyme may be introduced to act as a catalyst. This could last from 10 to 20 days.

● In the 2nd chamber, the mixture is allowed to undergo further digestion. There is no longer active mixing in order to promote separation, and there is no need for heating as the process generates its own heat. Here’s where the gas one starts to accumulate in the gasholder.

● Finally, in the last chamber, the settled sludge is dewatered and thickened. The goal is to separate as much water as possible to decrease the volume of material. Finally, a phase known as sludge stabilization reduces the level of pathogens in the residual solids, eliminates offensive odors, and reduces the potential for putrefaction.

The entire process ends when the purified water is released back to the ground, or you can choose to connect to irrigators, the slurry/ fertilizer is collected in a gulley, and gas is released for use as biogas.


Bio-Digesters in Kenya

Affordable Housing in Kenya

What is a Bio-Digester?

Understanding Anaerobic Digestion

Anaerobic digestion is a collection of processes by which microorganisms break down biodegradable or organic material in the absence of oxygen. The process is used for industrial or domestic purposes to manage waste or to produce fuels that can be used in the day to day lives of people.

Anaerobic digestion occurs naturally in some soils and in the lake and oceanic basin sediments, where it is usually referred to as anaerobic activity. But with the digester, the process is aided and hastened by the environment surrounding it.

The digestion process begins with bacterial hydrolysis of the input materials. The feeding material that gets into the digester on the form of animal waste, grey or black waste is subjected to decomposition. Insoluble organic polymers, such as carbohydrates, are broken down to soluble derivatives that become available for other bacteria. Acidogenic bacteria then convert the sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids.

In Acetogenesis; the second phase, bacteria convert these resulting organic acids into acetic acid, along with additional ammonia, hydrogen, and carbon dioxide. Finally, methanogens convert these products to methane and carbon dioxide, which we then refer to as biogas.

As part of sewage and wastewater treatment, anaerobic digestion plays an integral part in reducing pollutants and harmful emissions of gas into the atmosphere. It also protects the environment ecologically by cleaning the air and the water released from the Bio-Digester.

A further treatment plan for the air exposed to the atmosphere, the gas can be further heated to produce safe gas-quality biomethane. It is combined with heat and upgraded to power steering fuel that is road efficient. The nutrient-rich digestate also produced can be used as an organic and natural fertilizer.

With the re-use of waste as a resource and new technological approaches that have lowered capital costs, anaerobic digestion has and still is a leading waste treatment plan.

Digestate from wasterwater treatment
Digestate from wasterwater treatment [CC BY-SA (]

Engineering the Digester

Anaerobic digesters can be designed and engineered to operate using a number of different configurations and can be categorized into batch and continuous process mode, mesophilic vs. thermophilic temperature conditions, high vs. low portion of solids, and single-stage vs. multistage processes.

For the batch process, the initial investment is considerably more than for any other process. This is because you need large tanks to store the batches of organic matter so it doesn’t interrupt the decomposition of waste and production of gas. With continuous however its more economical because you only need one large tank to cater to the waste.

Above all, for a thermophilic system, you need high levels of heat to maintain and hasten the process of digestion. Unlike mesophilic which can decompose in cooler temperatures but takes a long time for the waste to digest. Fortunately, with the mesophilic system, the output of gas is higher in methane than the other because it had more time for the gas to collect.

Finally, for the single-stage, all four processes required for anaerobic digestion can be accommodated under one go. But, with the multi-stages, there needs to separation to allow the reactors to completely partake in the methanogenesis and hydrolysis phases.

Batch or Continuous       

Because many people either have digesters under this category, we shall take a closer look into its engineering. In a batch system, the biomass is added to the digester to commence the process of digestion. From there, all the contents are sealed to withdraw any oxygen from entering.

For every batch, the scenario is usually predictable as to when the byproducts will be available. That is when the reactors will be opened to take out the slurry and the gas; otherwise, there will be an emission of harmful gases, severe and pungent smells erupting from the digester because of an incomplete process.

So, batch system is seen as a simpler and cheaper digestion process because you can estimate and anticipate biogas production over time.  With continuous digestion, you keep adding the waste even in the midst of the process and you rely on first in first out process which could not produce the best by-products. Either way, you can have a continuous supply of biogas.

Wastewater Treatment as a Bio-Digester Application

At this point, you have read about the process of waste treatment and you’ve also learned about the engineering process. So, now you will learn about why this treatment is the better option for wastewater treatment and management.

  • Replacement of fossil fuels – the biogas produced can easily be used to replace the available fuels.
  • Reducing or eliminating the energy footprint of waste treatment plants – septic tank has served its purpose, now the digesters have their time.
  • Reducing methane emission from landfills
  • Displacing industrially produced chemical fertilizers
  • Reducing electrical grid transportation losses
  • Reducing the usage of LP Gas for cooking
  • Ecological to the environment

Waste & Wastewater Treatment

At this point, we have already established that anaerobic digestion is particularly suited to convert organic material to useful industrial and home effluents. Instead of letting waste and sludge be dumped at sea, dumped in landfills, or burnt in incinerators, this waste management has provided a very vital solution to all these issues.

Pressure from environmentally-related legislation on solid waste disposal methods in developed countries such as the UK and Germany has increased the application of anaerobic digestion as a process for reducing waste volumes and generating useful byproducts. In such areas, they are called biological mechanized treatment plants, where they indulge in saving the environment and treating waste on a large scale.

So, if the putrescible waste processed in anaerobic digesters were disposed of in a landfill, it would break down naturally and often anaerobically. In this case, the gas will eventually escape into the atmosphere. As methane is about 20 times more potent as a greenhouse gas than carbon dioxide, this has significant negative environmental effects. Hence the need to pressurize it in gas cylinders to use for cooking.

Certainly, in countries that collect household waste, the use of local anaerobic digestion facilities can help to reduce the amount of waste that requires transportation to centralized landfill sites or incineration facilities. This reduced burden on transportation reduces carbon emissions from the collection vehicles. Something even developing countries should emulate to avoid dangerous dumpsites everywhere.

Lastly, since the gas emitted from the digester can be used as a fuel. It can significantly be used to support electrical systems in the country. Moreover, these may even be hooked to the national grid,  in an industrial capacity, to avoid constant outages and blackouts.

Treating Waste Ecologically

Above all, sanitation is a very sensitive topic, practicing hygiene can go a long way in preventing diseases from erupting as well as other pandemics. That is why investing in a good wastewater treatment plan is essential. Luckily, with the bio-digester, your waste is treated effectively in a way that also produces beneficial products for use industrially and at home.

Digester Wasterwater Treatment
Article Name
Digester Wasterwater Treatment
Digester Wastewater treatment and management is a large topic that is yet to be discussed fully, and this article will try and cover some ground on that.
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Ishibox Limited
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