Sewage Parameters 4 Part 2: Phosphorus (P)

Welcome back,

Last time we discussed Phosphorus (P) in its different forms and why it is important as regards package wastewater treatment.  It is frequently being specified as an effluent parameter at levels from 0.5 – 5 mg/l.

The easiest way to decrease P in sewage effluent is to investigate if a specific cause of high P levels can be identified.  For example, in a hotel that still washes its own laundry, switching to a low P detergent can markedly reduce P levels in the influent and thus effluent.

Some reduction of P will naturally occur in the Primary settlement area of a package sewage treatment plant such as the Blivet.  Some P is adsorbed onto Suspended Solids (SS) and thus settling out SS will lead to a small reduction in P in the effluent.

Phosphorus can be reduced by both biological processes such as the Bardenpho process or during denitrification.  However, the most usual method used in package sewage treatment is by dosing the system with Aluminium/Ferric Sulphate (FeSO4).  FeSO4 reacts with P in sewage and forms a flocculent, which settles out into the sewage sludge.  The level of reduction of P, all things being equal, is a function of the amount of FeSO4 introduced in the sewage treatment system. 

FeSO4 lends itself to package sewage treatment in that package plants such as the Blivet, can have a small dosing pipe fitted directly into the primary settlement area, thus allowing relatively easy and safe dosing.

FeSO4 is unfortunately a hazardous chemical and thus adequate health and safety precautions need to be taken when servicing or operating a system.  FeSO4 is usually supplied in an IBC in a bunded area.  As FeSO4 is a hazardous and corrosive chemical overdosing of a biological system, such as the BMS Aerotor, can result in bacterial death and impaired performance of the system. Even at optimum dosing it will negatively affect the biofilm growth, which treats the sewage.  There can be a considerable lag period between the system completely recovering and FeSO4 overdosing being detected and stopped.  The other main drawback of dosing with FeSO4 is that it increases sludge bulk by 20-25%.  This means that the periods between desludging can be considerably reduced if adequate allowance is not made.

A sample Ferric Sulphate dosing calculation for Phosphorus reduction can be see below.

Next up for discussion is Ammonia (NH4).

If you have any questions of would like information on package wastewater treatment products, please do not hesitate to contact us.

A bit about the company:

BMS is a quality manufacturer of package products for wastewater and stormwater treatment. BMS started in 1986 and has exported products to over 50 countries around the world.  It is a third generation family business with huge expertise in wastewater and stormwater.
BMS manufacture a full range of products for surface water and wastewater treatment including our pioneering next generation RBC system the Aerotor, which forms part of our world leading Blivet package sewage treatment plant, a ‘one stop shop’ for all surface water products from design to installation including attenuation, interceptors, holding tanks (incl. chemical resistant), hydrobrakes, rainwater harvesting tanks & vortex silt/oil/debris separators, fully fitted pumping stations, our plug & play vehicle wash water recycling system; the Recyclone and much more.  All BMS products manufactured in our ISO 9001 factory are made using solar energy from our own PV system. 

BMS also can provide a Free Design Service for Sewage Treatment, Pump Stations or Surface Water and a full O&M, Repair, Advice and Testing service for existing installations.  We also can do free CPD Presentations on Sewage Treatment/Surface Water Management at any location. 

We would be delighted to discuss any requirements you might have and we are available to meet you at your convenience.  Please do not hesitate to contact us.

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