For some applications, it's important that the glass fibres have fewer impurities, however, this involves additional steps in the manufacturing process. Other materials can be used to give exceptional strength and at the same time be much lighter... Kevlar and Carbon fibre are examples. They are expensive to manufacture and are not needed when it comes to making tanks and containers as GRP is the economic material of choice.
Where brick, concrete and steel were the materials used before to build underground tanks, they are now GRP or fibreglass. After the second world war someone realised that by mixing threads of glass with resin a strong light material could be made. As glass is resistant to most corrosive materials the glass reinforced plastic (GRP) could be moulded to form any shape, and in the case of septic tanks, used to separate solid sewage from the liquor.
60 years ago Klargester used this material to make GRP septic tanks and later cesspools and eventually many of the huge tanks we see transported on the roads today.
There are septic tanks functioning well enough after 50 years but it is the Gravel soakaway which fail. They simply fill up with black organic matter and 15 years is about the average life of the soakaway.
Conversion units such as the Allerton ConSept use blown air to encourage aerobic bacteria , transforming the septic (anaerobic) regime into an aerobic one where the treated effluent can, with Environment Agency permission, be discharged into the river system. If no ditch is available, the ConSept utilises the air to lift, by siphonic action, the cleaned water to the surface. A shallow soakaway is far more effective than one deep in the ground.
It is worth noting that raw sewage has a value of about 300ppm. What comes out of a well maintained septic tank is 200ppm of horrible black water, but water which carries two thirds of what went into the tank!
Generally, sewage treatment plant (and the ConSept too) have to produce a final effluent of just 20ppm before it can go to the River system. Rainwater is about 5ppm.The ConSept works well in brick septic tanks but apart from the difficulty in removing the GRP Septic Tanks baffles, once inside the tank it is as if you have a brand new sewage treatment plant. Half the price and no machines on the lawn!
There is a downside for this of course: a capital cost of about £3000 and running costs of around £300 which includes servicing by Allerton, de-sludging every 12 to 24 months and electricity.