Sewage Treatment Plant Ultimate Guide

Sewage Treatment Plant

Sewage treatment plants can be a minefield to most people when trying to choose one to have installed at your home. That’s why we have decided to write up this awesome all you need to know information page to help you out. We know from our years of experience that almost all manufacturers will tell you that their treatment plant is the best. However, we don’t think it’s as simple as that because at Xoli we prefer to ask what is important to you. We will provide you with the honest information on the options available to you and allow you to decide which sewage treatment plant best fits your needs. We provide innovative waste water solutions to reduce environmental pollution.

Ultimate Guide contents

What is a Sewage Treatment Plant?

In simple terms a package sewage treatment plant is a smaller version of your large local authority treatment works. They work in a similar way to a septic tank with the addition of secondary treatment and sometimes tertiary treatment. Due to septic tanks releasing a very polluting effluent quality there is a big push to move towards package treatment plants. It is within this second stage treatment process that the world of wastewater treatment plants really opens up. This is due to the vast variety of treatment methods available. Basically this treatment phase aids the growth of bacteria to breakdown the waste into far cleaner effluent. This is much better for our environment after the water is discharged from our home treatment plants.

When would I need a Sewage Treatment Plant?

You will need a treatment plant if your home is in an area with no access or connection to the main sewer network. You will also need a package treatment plant if you need to upgrade an existing septic. Reasons for having to upgrade would be to come inline with the changes to the General Binding Rules 2020 or if your existing system is failing.

Best Domestic Sewage Treatment Plant

As per our introduction what we at Xoli perceive to be the best package treatment plant in the market is really irrelevant. The reason for that statement is that it is extremely difficult to have a one system fits all approach given the varying factors to consider with each individual application. Every person and every site has different needs and restrictions. Everything from ground conditions, final effluent levels, power consumption, maintenance costs, budget, visual impact, noise, etc. Therefore we have decided to give you a thorough rundown on the various types of treatment systems available. This will provide you with more of an understanding and empower you to decide what the best domestic sewage treatment plant will be for you!

Types of Sewage Treatment Plant :

All of the above types of domestic treatment have different ways of treating the incoming waste water. Waste water is everything that comes through your foul waste pipes in your home. i.e sinks, basins, washing machine, toilets and showers. This section will explain each systems treatment method and some of the advantages and considerations of each system.

Activated Sludge Plant

The Activated Sludge Process is a common method used for sewage treatment. It is simply a suspended growth biological treatment process using aeration to keep bacteria in suspension which treats the sewage . Tanks have a bio zone chamber and a settlement chamber. The treatment process takes place in the bio zone, treated sewage enters the settlement zone before discharging the treated wastewater. Treatment plant shown here is a Premier Tech ASP

Here’s how it works:

ASP Sewage Treatment Plant

Step 1. The plant accepts and treats incoming sewage in the central bio-zone, with use of the extended aeration principle

Step2. A simple course diffuser, housed in the draft tube, introduced the air from the integral blower that provides the oxygen to the bacteria, which ten treat the sewage.

Step3. The Bio-zone then retains the mixture of sewage and bacteria until the level of treatment has been achieved.

Step4. The treated final effluent then enters the settlement zone where settlement takes place. the settled solids are drawn back towards the draft tube, housing the diffuser and are returned via the airlift principle to the bio-zone for further treatment.

Step5. The treated final effluent leaves the plant over a weir at the outlet level, that extends around the circumference of the tank. The movement of the fluid through the whole system is only by gravity displacement.

Activated Sludge Plants are a low cost solution. There are no mechanical or electrical parts within the tank. Operated by a compressor and timer usually in a sealed pod within the neck of the tank or external pod.

Benefits: Low purchase cost, Low maintenance costs, low visual impact

Consider: Electric running costs may be higher than other types of systems – ask manufacturers for electric consumption figures

Installation costs – may be more expensive than other systems – site conditions can affect installation costs

SBR – Sequential Batch Reactor Sewage Treatment Plant

This method of treatment is very clever and gives total control over effluent quality. Effluent is the term we give to the outflowing treated water. It treats the incoming waste water in batches. Usually a two chamber or sometimes a partial single chamber system. Examples shown are Roto Ecobox and Premier Tech Aqua Solido Smart

Here’s how it works;

SBR Sewage Treatment how it works

Step 1. Wastewater enters the tank chamber 1

Step2. Wastewater is transferred by air lift to chamber 2

Step3. Intermittent aeration takes place in chamber 2

Step4. Treated effluent is discharged from chamber 2 by air lift

Step5. Sludge returned from chamber 2 to chamber 1

SBR Systems are very similar to a sewage treatment works where the untreated wastewater undergoes a complete cleaning cycle before being discharged. Two chamber systems are usually programmed to carry out four cleaning cycles per day, each cycle lasting 6 hours, whilst single chamber systems tend to carry out two cleaning cycles per day each cycle lasting twelve hours.

SBR systems are a plug & play systems. Operated by advanced controller technology, pre set by manufacturers and very user friendly. SBR systems are operated by air via a compressor and have no mechanical or electrical parts within the tank. Controllers and compressors are usually mounted in a control cabinet which is remote from the tank and can be mounted either externally or internally up to 20 mtrs from the tank. The configuration can vary from manufacturer to manufacturer. Some manufacturers have the compressors mounted in sealed pods within the tank with the controllers mounted remotely.

User friendly SBR Controllers

Benefits: Plug & Play, No mechanical or electrical parts in tank, low maintenance costs, low energy consumption, low visual impact, high cleaning performance, holiday mode, more control of system, low installation costs

Consider: Initial purchase cost may be higher than alternative systems, external cabinet/controller visual impact

Fixed Bed Bioreactor – FBBR

Fixed Bed Biorector systems use a combination of specially designed plastic filter media with aeration to treat sewage. Systems are normally a three stage process comprising of a primary settlement chamber, aeration chamber and final settlement chamber. Example Tricel Novo.

Here’s how it works;

Tricel Novo Domestic Sewage Treatment Plant
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1.Wastewater from the dwelling, toilets, sinks, shower etc., enters the plant.

2.Effluent enters the primary settlement chamber. Settlement occurs when the heavier solids drop out of the wastewater and settle to the bottom of the tank to create sludge, and the lighter solids float to the top of the water to create a scum. The top layer acts as a seal and stops odours escaping. This chamber separates up to 70% of the solids present.

3.Next is the aeration chamber, where masses of naturally occurring bacteria inhabit specially designed plastic filter media. The bacteria feed on the waste removing it from the liquid. A continues supply of air from a low pressure, high volume compressor in the top section of the unit sustains these bacteria. Wastewater passes through the filter media over and over, ensuring a very high treatment efficiency.

4.The liquid then proceeds to the final settlement chamber. Any remaining minute bacterial particles separate from the liquid within this chamber before discharge from the plant. This process slows the liquid’s velocity, allowing for any final trace impurities to settle to the bottom of the tank section. A sludge return system then returns these impurities back to the primary settlement chamber.

5.The remaining treated liquid now meets the required standard and is safely passed out of the Tricel Novo plant system. The treated effluent is now ready for discharge to a suitably designed discharge area as required by the relevant local authority.

Tricel Novo How It works Video

Benefits: Compact design, robust tank, reliable, low installation costs, low maintenance costs,

Consider: visual impact – control panel/compressor housing above ground level, compressor runs 24 hours per day

Moving Bed Bioreactor

Moving Bed Bioreactor or MBBR sewage treatment plants are very similar to fixed bed bioreactor systems. The main difference is that the media within the treatment chamber is loose allowing the pieces to move freely within the chamber. MBBR package treatment plants tend to have 3 chambers. A primary chamber, treatment chamber and final settlement treatment. Biofilm carrier media offer a habitat for bacteria to live and reproduce resulting in better cleaning performances and longer bacteria lifespans. Example shown below ids the Premier Tech Aqua SAF sewage treatment plant, typically used in applications of above 25pe

Moving Bed treatment Plant

Here’s how it works;

  1. The incoming wastewater enters the primary settlement zone
  2. Wastewater flows into the biozone via a built in impingement filter which prevents solids entering the biozone. This is combined with forward flow via airlift (controlled by a solenoid valve and timer. The Biozone contains a number of sections which loss plastic media which encourages growth of bacteria and biomass which treat the wastewater.
  3. Air is introduced below the media from above ground blowers. This air fulfils the requirement for oxygen and also scours the media which removed excess biomass
  4. The combination of treated wastewater and excess solids are then transferred forward into the humus settlement zone. Here the humus settles to the bottom of the tank with the treated wastewater being discharged at the top. The heavier solids are recycled to the primary zone (controlled by a solenoid valve an timer)
  5. The treated final effluent leaves the plant via the dipped outlet pipe. The movement of fluid through the full system is by gravity displacement.

Benefits: Reliable, cost effective system with energy efficient blowers, minimal visual impact. no below ground moving parts

Consider: Installation costs

Rotating Biological Contactor / Rotating Disc System

Rotating Biological Contactor / Rotating Disc Systems are manufactured by Klargester and is the only packaged sewage treatment plant utilising rotating Biological contactor technology. The (RBC) is central to the operation of this type of plant. The RBC comprises of banks of vacuum formed polypropylene media attached and supported by a steel shaft. This Media provides a large surface are which aerobic micro-organisms establish themselves and breakdown the sewage. Here’s how it works

Klargester Biodisc

Wastewater flows into primary settlement zone (1) where solids are retained and settle.

Partially clarified wastewater containing suspended solids flow upwards into the first stage Biozone (2) for breaking down by micro-organisms on the RBC.

Suspended solids are returned to the primary settlement zone whilst treated effluent is transferred to Biozone (3) for further treatment.

Finally, any remaining solids settle in the final settlement (4) and treated effluent is discharged.

How a Klargester Biodisc works video

Benefits: Proven system, High Cleaning Performance, Low Running Costs

Consider: Maintenance Costs, Spare Parts Costs

Non-Electric Sewage Treatment Plants

Non-Electric Sewage Treatment Plants are very similar to the above domestic treatment plants with one key difference. They do not require any power supply to operate the system. Non-Electric package treatment plants normally consist of 2 chambers. The first chamber is a primary settlement chamber, the effluent flow by means of gravity through into the treatment chamber. It is within this chamber where the treatment of the effluent happens by passing through media. Naturally occurring bacteria grow on the media which feed on the effluent and produce cleaner water. Meaning these units are often installed after existing septic tanks as a retro-fit to improve the discharged effluent quality.

The image below showcases the above process really well.

Benefits: No Electricity Required, Low Running Costs, Completely Silent, Excellent Effluent Quality, Long Absence Periods Acceptable

Consider: Initial purchase cost,Invert Depth of Outlet (may require a pumped out which would require power)

Gravity System or Pumped Outlet System?

Should i buy a gravity or pumped outlet system? This is actually very straight forward. If the area of discharge is higher than the outlet of your septic tank or sewage treatment plant you will need a pumped outlet or sewage pump station and if not a simple gravity outlet will do the job.

Some manufacturers offer their treatment plant with a built in pump i.e pumped outlet, whilst others offer a separate pump station.

Sewage Pump Stations
Single Pump Station

Benefits of pumped outlet: Integral part of treatment plant, programmed and factory set, covered with treatment plant warranty.

Consider: Access and maintenance of pump

Benefits of Pump Chamber: Access for maintenance.

Consider: Installation costs, set up, warranty period

Sewage Pump Stations

Sewage Pumping Stations come in various shapes, sizes and specifications. So getting the right package pump station for your system can sometimes be tricky. However, that’s where Xoli will help you out, we can help you purchase the most cost effective pumping station for your specific needs. Contact Us for a solution today.

How do Sewage Pump Stations Work?

Sewage Pump Stations work automatically as soon as they are connected to a power supply. Sewage or wastewater collects in the chamber or tank, when it reaches the set max level the float switch is tripped. The pump then kicks in and creates enough pressure to draw the waste water from the tank through the pipe to the discharge point. Discharge areas could be to tertiary treatment systems, raised mounds, the main sewer line, ground soakaways and many others. Sewage Pump Stations can be installed independently for discharging sewage from your house or commercial premises to the main sewer network. They are often installed after a septic tank or a sewage treatment plant.

Sewage Treatment Plant Cost?

How much does a sewage treatment plant cost? Is obviously a very common question we get asked however it is not a simple straight-forward answer. Prices for domestic sewage treatment plants can range from around £1700 to £5000. Depending on your site conditions and requirements as an individual it is important to keep in mind that lowest purchase cost is not always the best. The same can be said for the most expensive purchase cost. This doesn’t necessarily mean it will be the best for you either. When evaluating the cost of a package wastewater treatment plant it is really important to consider the overall cost of the system including the materials you will need for installation.

See a simple example below;

Sewage Treatment Plant Cost Comparison

Some package treatment plants require less materials for installation than others depending on site conditions. Manufacturers installation instructions and/or site conditions may dictate the requirement for a concrete base & back-fill. This can add to the cost of installation (as this tends to mean more time on site for installation as well as the cost of material itself). Ground conditions play a massive part in how much your sewage treatment plant will cost. Location of your site will also play a part in the cost of your domestic sewage treatment plant. Different areas of the country have different requirements in what the acceptable effluent discharge levels are. This is where the cleaning performance of your system comes into focus.

Running Costs

Running costs: running costs of wastewater treatment plants should also be considered before you purchase. Whilst all systems should be maintained and serviced at least once annually and emptied when appropriate. There will be other factors to consider here as well like electricity consumption, maintenance and spare parts costs.

Final Effluent Levels

Final Effluent levels: Although Treatment plants have to comply with EN12566-3 and achieve minimum final effluent results of 20mg/ltr BOD: 30mg/ltr Suspended solids : 20mg/ltr NH4. Treatment plant final effluent values vary from manufacturer to manufacturer. These levels vary from achieving the minimum requirements of 20:30:20 to very high levels of cleaning performance e.g 5:13:0.7.

Final effluent levels can be a factor in the purchase cost of the system, due to the type of process, tank size and controls used by the manufacturers. However, this is not always the case. The most expensive does not always provide the best cleaning performance, nor does the lowest cost provide the minimum cleaning performance.

Final effluent level requirements will vary from region to region throughout the UK. Therefore, It is very important clarification is sought from your local Environment Agency before purchasing your system. How and where you intend to discharge to and the levels required by your local agency will be a big factor in the choice and cost of your treatment plant.

Installation of package Treatment Plant

Installation of Sewage Treatment Plant’s should always be carried out by a professional company with experience in this field. When having a sewage treatment plant installed for your home and business there are many things to consider, making it important to have a business who is experienced guide you along. Thankfully Xoli can help in various ways with installations of Sewage Treatment Plants throughout the Scotland and the rest of the UK.

Sewage Treatment Plant Size Calculation

Sewage Treatment Plant Size Calculation can be complex for some applications thankfully for the majority it is pretty straightforward as you will see below. If you have a need for a commercial sewage treatment plant for a hotel, glamping site, caravan site, multiple houses, residential care home, etc we can help you out. Simply give us a call. For standard domestic sewage treatment plant applications you can use the simple infographic below or read British Water Flows and Loads.

Sewage Treatment Plant Size Calculation
Wastewater Treatment Plant Design

Sewage Treatment Plant Permissions

Sewage Treatment Plants do require certain permissions and must be installed according to the relevant guidelines.

Regulations, guidelines and information can be found on the links below;

Water Environment (Controlled Activities) Scotland Regulations 2011

SEPA Septic Tanks and private sewage treatment systems

SEPA CAR practical Guide

Environment Agency General Binding Rules

Natural Resources Wales permits and permissions

Northern Ireland DAERA

Tertiary Sewage Treatment

Tertiary Treatment of your domestic sewage treatment plant comes in various forms which we will explain in this section. This treatment is basically the final treatment stage before the effluent is discharged to ground or back to the watercourse. Now we will explain each tertiary treatment method below;

Soakaway – Drainage Field

Sewage Treatment Plant Drainage Fields sometimes referred to as a soakaway is an arrangement of perforated pipework. This pipework is placed in trenches over drainage stone. The concept is that the effluent can trickle through the perforated pipe into the ground for further treatment by the bacteria in the soil. Like with any sewage treatment plant installation it is imperative to have a Ground Porosity Test carried out. The reason being, is that the size of drainage field required is based on your Vp value which you can only obtain from your Ground Porosity Test. It is worth noting, soakaway crates cannot be used for the discharging of sewage effluent. Soakaway crates must only be used for rainwater or surface water drainage. This is as per the UK’s general binding rules.

What Size of Drainage Field do i need?

Simple really. The Vp value multiplied by the Number of persons (P) multiplied by a factor (0.25 for Septic Tanks, 0.2 for Sewage Treatment Plants) will give you the Area (A) required in Sq. Mtrs. Laid in 600mm wide trench divide Sq. Mtr. by 0.6, This will give you the pipe length required. e.g.

Septic Tanks : A= Vp x P x 0.25

Sewage Treatment Plants : A = Vp x P x 0.2

We have created a great resource for you below;

SewageTreatment Plant Soakaway Sizing Guide

We can supply ready made drainage field kits see our soaxaway kit for prices and more information.

Tertiary Treatment Units

Tertiary Treatment Units can come in various forms depending on the manufacturer. There purpose is to further treat the effluent before it enters back into the water system either via watercourse or ground water table. Tertiary Treatment Units use a much smaller area than traditional drainage fields. We supply 2 different types here at Xoli as below;

Tricel Puraflo

Tricel Puraflo Tertiary Treatment units can achieve tremendous cleaning performance to reduce environmental pollution. These tertiary treatment units use a peat fibre biofilter system making it one of the most sustainable wastewater treatment systems on the market today. Puraflo units are installed after a septic tank or Sewage Treatment Plant where the effluent flows into a small pumping chamber before being pumped into the Puraflo modules. This allows even distribution of the effluent over the peat fibre material to give maximum cleaning performance. Learn about how the Tricel Puraflo Tertiary Treatment Units work by watching this short video. Or have a look on our dedicated Tricel Puraflo Page.

Ecoflo Coco Filter Tertiary Treatment Unit

Ecoflo Coco Filter Tertiary Treatment Units require no electricity at all to operate and achieve high cleaning performance. These Tertiary Units are quick and easy to install after your domestic sewage treatment plant or existing septic tank. The Ecoflo Coco Filter Units use a revolutionary system using coconut husk fragment-based filtering media. A natural organic material which treats the wastewater using no energy. Learn more about the Ecoflo Coco Filter Tertiary Treatment units on our dedicated Ecoflo Coco page or by watching Ecoflo Coco Filter How it Works.

Raised Mounds

Raised mounds are another option for ground discharge and commonly constructed and applied in areas where soil porosity levels are poor. As the name suggests raised mounds are above ground and constructed of layers of sand, gravel and pipework to create a soakaway. Here’s an example of what a fully installed raised mound looks like;

Sewage Treatment Plant Raised Mound Installed
Raised Mound

Sewage Treatment Plant Maintenance

Do i need to maintain my sewage treatment plant? In short the answer is YES. Whilst most sewage treatment plants are designed to be very user friendly they will need maintained. Like with everything in life, if something is looked after properly the lifespan will be longer. This can be said with Sewage Treatment Plants as well.

Lack of maintenance or no maintenance can result in blockages and failures of soakaways if discharging to ground, or pollution of our watercourses if discharging direct to a watercourse. Pollution will result in a fine from the Environment agency.

Download this great guide on how to look after your Wastewater Treatment Plant between service intervals.

Ensure you have your treatment plant serviced regularly – It is crucial for our environment that we all play our part in reducing pollution

We can an offer a sewage treatment plant maintenance package to suit you needs simply call us or drop us a message to get a quote.

Sewage Treatment Plant Emptying

All Sewage Treatment Plants like Septic Tanks do require emptying at some point. You will read a lot of mis-information in the market about emptying intervals for various sewage treatment plants. Emptying intervals will vary on each system depending on usage. Therefore it adds more importance to having your treatment plant serviced at the appropriate intervals. We can arrange your tank emptying here.

Grease Traps

Grease Traps are very important to aid the performance of sewage treatment plants. Fats, oils and grease do not belong in the drainage network. Whether that is the main network or a sewage treatment plant. Costly blockages and pipe damage are regularly caused by build up of FOGS. However, installing a grease trap will minimise this. Grease traps are available in various forms from above ground, under sink and below ground solutions. Grease traps should be used for households and commercial premises. Commercial Catering venues such as Restaurants, Hotels, Wedding Venues etc. will have a greater need. For such venues a Grease Trap is very important to main our drainage network. It is especially important if you are connected to a Septic Tank or Sewage Treatment Plant.

Grease Traps are simple units and very effective at preventing excess FOG’s entering the drainage system. Installed before your sewage treatment plant or discharge point to main network, grease separators retain grease and fats protecting your drainage system. Slowing down the flow of hot greasy water allows suspended FOG’s to cool and separate. FOG’s float to form a scum layer at the surface with large solids settling to the bottom of the tank. We have a full range of Grease Traps available for despatch or install throughout the UK.

Here is Scottish Water’s fantastic video explaining the importance of avoiding FOG’s.

Grease Traps

Septic Tank Upgrade – 2020 Rules

Changes to the way Septic Tanks can discharge came into place January this year in England and Wales. The same regulations do not apply in Scotland yet. We feel SEPA will take a similar course of action in the future. In short, you can no longer have your existing Septic Tank discharging directly to a watercourse. If you are you must look to find an alternative method of discharge or upgrade to a package sewage treatment plant. Official General Binding Rules 2020.