BIODIGESTER SEPTIC TANK

How Does a Biodigester Septic Tank Work

Biodigester septic tanks break down waste matter into water, carbon dioxide, and methane gas (biodegradation). When wastewater comes into the tank, special bacteria in the tank feed on it converting it into water, gas, and sludge. The sludge settles down and continues decomposing gradually while water and gas can be collected for other uses.

Biozone biodigester septic tanks have three crucial parts, grease interceptor, biodigester tank, and spillage drain.

Note that sewer water is a mixture of toilet flashed water known us blackwater (water in contact with fecal matter) and kitchen, bathroom, floor traps, wash& basin known as greywater.

The greywater contains harmful substances like oils, grease, and detergents. It goes through the grease interceptor to remove these substances after which the now clean water goes to the spillage drain (soak pit) for further treatment from where it can be used for irrigation.

The blackwater goes into the biodigester tank where bacteria and enzymes are introduced to feed on the solid part while cleaning the water. The solid part settles into the bottom from where decomposition takes place producing water and gas. The water goes to the soak pit while the gas can be vented into a special chamber for further conversion into cooking gas or released into the atmosphere.

Note that only Biozone biogas digesters can be used to produce enough gas which can be used for domestic purposes. Biozone biodigester septic tanks produce methane gas in small quantities which is released into the environment as it cannot be used for any other purposes.

The soak pit can be perforated to allow the water to soak into the soil or the water can be drained using pipes to be used for irrigation. This water is rich in nutrients which make it good for plants and vegetables. However, this water is not fit for domestic purposes or animal use because it still contains some trace minerals harmful to humans and animals.

How to Design a Biodigester Septic Tank

Several Factors affect the choice of a biodigester design this include but not limited to:

• Clients Budget – the non-mechanical biodigester is cheaper than the mechanical biodigester.
• Intended use of water effluent – water effluent from a mechanical biodigester can be used for irrigation and cleaning as it meets the NEMA minimum requirements. Water effluent from the non-Mechanical biodigester is disposed in soak pits
• Soil condition- in places where the soil is either shallow or doesn’t absorb water easily the Mechanical biodigester is recommended.
• Population- no of people intended to use the same biodigester.

HOW TO CALCULATE BIODIGESTER SEPTIC TANK VOLUME / SIZE

The Volume of a biodigester is determined by considering the followings Factors-Estimated waste water volume

The Waste water volume is estimated by considering-

• Population (Volume= Population x 100liter per person per day)
• No of units (Volume=No of Units x 500liters per day).
• Retention time
• Possibility of future expansion

Common Concrete Biodigesters in Kenya

They are made from durable concrete and can be precast or onsite concrete biodigester and handle larger volumes of waste compared to plastic. Most of the manufacturers make small sizes ranging from 1m3 to 4m3 and are single chamber biodigester.

Advantages of Concrete Biodigesters

• Durable and has strength
• The system is built out of reinforced concrete giving it structural strength that can withstand pressure.
• Ease of installation
• They are designed for easy installation especially the precast that simply requires dropping the precast unit into place, requiring minimal on-site labor and construction.
• Long lifespan
• Concrete biodigester are designed to last for decades with proper maintenance
• Space efficiency
• They can be designed to fit compact spaces, making them suitable for both urban and rural settings
• Short Installation Time for the precast.

Disadvantages of Concrete Biodigesters

• Higher initial cost:
• The cost of biodigester, installation and infrastructure modifications.
• Limited Design Flexibility
• Precast is often manufactured to specific shapes and sizes, which can limit design option.
• Transportation Cost:
• They can be heavy and bulky making transportation to site a challenge especially for large projects and can also get damaged during transportation.
• Installation and connection issues:
• Improper installation and faulty joint connections can lead to leaks and reduced efficiency of the systems.
• Not Flexible:

For precast, once installed poses a great challenge if there is need for modifications or expansion

Plastic Biodigesters in Kenya

They are ready to use septic tanks made of Pvc and are available in different sizes.

They are designed for residential use, managing wastewater sewage efficiently.

Advantages of Plastic Septic Tanks

• Resistance to corrosion and cracks.
• Lightweight: Easy to transport and move and does not require heavy machinery for installation or transportation.
• The lids and connections have a snug fit and do not allow the water to seep outside the tank.
• They are cost effective

Disadvantages of Plastic Septic Tanks

• Breakage during installation: They are lightweight and can be damaged during installation. They need careful handling to avoid breakages.
• If the installation is not done properly, the tank can float to the surface of the ground due to saturation of the soil if ballast is not installed.
• The plastic tanks can get deformed in certain types of soils. They are very sensitive to soil conditions and can break due to changes in temperature.
• They need regular inspection for effluent levels
• They can also break due to the weight of the soil or if the vehicles drive over the land where they are buried.

1. Clogging: Accumulation of non-biodegradable materials and discharge of effluent water that has a higher percentage of sludge. After about three years, this system develops numerous problems due to fats, oil and grease build up making relatively slower in functioning.

2. Overloading: This is a major problem especially with 1m3 systems that serve upto 1-15 persons. This exceeds the capacity of the system caused by exceeding the capacity of the system and also sudden influx of water due to heavy down pour.

3. Inadequate maintenance: They have small provision of inspection that makes the inspection and maintenance difficult. Lack of periodic inspection and maintenance leads to sludge build up and even back flow and bad odor.

4. Odor Issues: This is contributed by improper venting of the biodigester tank.

DIFFERENCES BETWEEN BIOZONE BIODIGESTER & OTHER SEPTIC BIODIGESTERS

• Biozone provides septic biodigesters have right capacity depending on the need of the client. They have large surface area that allows for sufficient time for settling of waste water to allow enough separation of wastewater and the sludge. Most of the companies provide small size single chamber biodigester that do not allow for enough time for complete separation of wastewater and the sludge.

• Biozone has a well-designed soak pit system that is fitted with filters and surrounded with a hard-core rock ensuring efficient water disposal. The company also installs at least two soak pits to act as a back in event of clogging/ suffocation. This ensure efficient functioning for our systems.

• The inspection chamber lids in Biozone’s bio digesters are large enough to allow for easy access during the systems inspection and maintenance. Whereas other companies provide for very small inspection points that make it very hard for regular maintenance.

• Biozone has specific enzymes to solve issues such oil accumulation, sludge accumulation and odor while the rest of the of companies have generalized enzymes that are not very effective.

• Biozone provides regular inspection and maintenances to their bio digester systems. The other companies after installation they do not offer these essential services to their clients.

• The first chamber of our system is fitted with grease trap that make our system handle both black water and grey water and still function optimum all. Whereas biodigester installed with other companies can only handle black water requiring separation of grey water.

• We offer innovative solutions that are customer tailored and cost friendly.

• We have the excellent workmanship that offers quality professional services within the stipulated time.

HOW TO CONSTRUCT BIODIGESTER / HOW TO INSTALL A BIODIGESTER

Site Preparation

1. Site Demarcation

Upon identifying the location for the biodigester the location should then be demarcated ready for excavations

• Clearance of site

Remove all vegetation and all objectionable organic material from the construction area, and burn or dispose of all such debris in tips

• Excavations

 Excavations are done ensuring that the capacity of the Biodigester is maintained

Blinding

Check the setting out, dimensions, alignment, thickness and the level for the

blinding. The blinding thickness shall be achieved as per drawing. The cast blinding shall be cured properly with covering wet hessian cloth. The blinding shall then be protected with a safety warning to prevent the cast blinding from damages that may cause by the working machinery.  surface of blinding shall be made smooth, repair of thermal cracks and make true levelling to receive concrete. Preparation of spacer for the next day for casting

Ground Slab

• Reinforcement

Fix the reinforcement steel as per the approved drawings, Use concrete spacer for bottom and vertical bars as concrete covers. Any loose binder or ties along the splice’s reinforcement steel shall be re-tightened. Bend inward the free ends of the binding wire.

• Concrete to be prepared

All concrete shall be waterproofed with a recommended water proof at a recommended ratio of one kg to one bag of cement. The concreting must be done with the necessary equipment or tools for concreting use such as vibrators, wood float, shovel etc. Clean the slabs for dust or any small particles or deleterious materials that may impair the workability of concrete.

Walling

There are two options of walling

1. Masonry wall

2. Reinforced concrete wall

Masonry wall

Foundation stone must be quarrying blue stone not ndarugo machine cut size. The mortar proportions shall be as recommended. The thickness of mortar joints shall be as recommended for both horizontally and vertically. The mortar shall be spread over the entire top surface of the stone; (over the front and rear shells). The mortar shall be raked out from the joints with a trowel of each course and is laid to a recommended so as to ensure good bond for the plaster. The height of wall to be done in a day’s work shall be restricted to 1 meter. The first course of masonry shall be laid with great care, making sure that it is properly aligned, leveled and plumbed, as this will assist the mason in laying succeeding courses to obtain a straight and vertical wall. Cleaning work area off loose material/concrete, Proper stacking of bricks/ blocks, Quality of Bricks/ sand, Wetting of bricks, Cleaning of dead mortar

Reinforced Concrete walls.

Formwork should be properly fastened to prevent budging. Standard of reinforcement type shall be as recommended vertical and horizontal bars. should be properly fastened to prevent budging thickness of the wall

Concrete shall be done to a recommend class.

Plastering

The mortar proportions shall be as recommended and to be cured for a minimum of 7 days. Waterproof should be done at the rate of 1kg waterproof to 50kgs Cement

Formwork

Props to be at recommended spacing of formwork to be free of leakages

Size of cover opening to be as recommended. Desired ground level should be attained

Slab Reinforcement

• Reinforcing should be as recommended especially for parking areas.

Concrete Casting

Thickness of the wall be as recommended Concrete class be prepared as specified.  Recommended curing dates are 21 days

Formwork Removal

Duration to removal of formwork to be a minimum of 14 days

Finishes

The covers levels to be specified for parking and garden. For garden medium density. covers to be used, for parking heavy duty manhole covers to used

The mortar proportions shall be as specified. To be cured for a minimum of 7 days.

Advantages of Biodigester Septic Tank

These are the benefits of biodigester septic tanks over normal septic tanks and pit latrines.

• Costs saving. Normal septic tanks require regular exhauster services which are expensive while biodigester septic tanks do not require such services.
• Decreased foul smell. Biodigester septic tanks have very little or no odor at all since almost all waste is broken down while normal septic tanks tend to be smelly.
• Little maintenance costs. Biodigester septic tanks require little or no maintenance as compared to normal septic tanks which need constant maintenance since they hold bulk waste material for long periods hence increasing wear and tear.
• Space requirements. Blueflame biodigester septic tanks require little space to set up as compared to normal septic tanks. This is because biodigesters hold waste for short periods before full treatment and biodegradation while normal septic tanks have to hold a lot of waste until they are emptied by exhausters.
• Biodigester septic tanks produce by-products like water and gas which can be reused for other services while normal septic tanks have no byproducts. The water from biodigesters can be channeled for irrigation services since it is rich in plant nutrients.
• Decreased environmental pollution. Biodigester septic tanks break down all organic waste and the by-products released to the environment are not harmful. Normal septic tanks on the other hand need to be exhausted and their contents disposed of somewhere else. These secondary disposal sites are big environmental pollutants. A case example is the Ruai sewage disposal site in Nairobi which has continually brought harm to the surrounding environment.
• Overflow risks. Biodigester septic tanks offer zero risks of overflowing, but normal septic tanks are prone to overflows since it is added to tell when they need exhausting. This is a health risk particularly in areas where flooding usually occurs. Many hygiene-related illnesses like cholera have been known to be more prevalent in areas with poor drainage and sewage systems.

Disadvantages of Biodigester Septic Tank

• Biocultural additions. Biodigester septic tanks need periodic additions of the bacteria and enzymes (e.g Septozyme BFB) that make the biodegradation process possible, while normal septic tanks do not require such additions.
• Material disposed of in biodigester septic tanks needs to be organic otherwise the biodegradation process will not be possible.
• The design and setup of biodigester septic tanks require a high level of expertise and technical know-how as compared to normal septic tanks.
• Biodigester septic final effluent mostly not fully treated to clean water that can be recycled to open environment as the same water require further treatment procedures.
• Biodigester septic Experiences a lot of shock loads due to un controlled contaminants from the households.

Note that although biodigester septic tanks may not be perfect, the advantages totally outweigh the disadvantages and it is therefore highly recommended for people to adopt biodigester systems as the way to safe and environmentally friendly disposal and management of waste.

As it can be seen from the above points, Biozone biodigester septic tanks are more useful than normal septic tanks and common digesters.

How to Convert Septic Tanks into Biodigester Septic Tanks

Normal septic tanks can be converted into biodigesters by restructuring them and introducing the right chemicals made of bacterial cultures and enzymes. Remember the work of biodigesters is to break waste material into gas, water, and sludge.

Once the biodigester enzymes and bacteria have been introduced into a normal septic tank or a pit latrine, they will quickly break the solid waste into gas, water, and slurry. Since the initial design cannot adapt to make use of the bi-products, the gas is released into the environment in very small quantities while the water sips into the soil. The little sludge left will settle at the bottom.

The main aim of converting normal septic tanks into Biozone biodigester septic tanks is to save on the costs associated with normal septic tanks. This conversion will make sure that your new septic tank will not fill up and bad odors are eradicated.

However, it is difficult to convert a normal septic tank into a biodigester for gas production. That is because household waste including bathroom and kitchen sink wastewater is not optimal for biogas production.