Bio-augmentation of fixed film filters
Once regarded as the main process option for the waste water treatment for small communities, circular biological filters, so common on the outskirts of towns for many years, provided a reliable low cost and low profile method of treating household waste water. Quiet and robust, their simple engineering and structural design could be easily maintained by a daily visit from an operator, who, on the smaller sites, only needed a couple of hours to carry out essential duties. Principal operating tasks involved de-sludging the primary and humus tanks, the remaining requirements revolved around general maintenance.
As new technology has developed, more opportunities for automation such as motorised distribution arms and automated de-sludging have occurred reducing the requirement for daily visits. However the lack of consistent site attendance can have an adverse effect on small remote works. The old daily rituals of weeding and pricking out often become neglected leading to inefficient distribution and build up of gross solids within the top surface of the beds, particularly if the media starts to deteriorate.
Dosing siphons, if not cleaned regularly can be extremely difficult for one person to clean if they block with fat. The maintenance of the sites then becomes more strenuous and time-consuming as a backlog of cleaning or maintenance has to be dealt with before the repair can be carried out. The problem sites start to sap funds and manpower to keep them running efficiently and operating within their EA consent. The drive for efficiency takes a backward step, as badly performing sites divert resources away from the more efficient sites that still require regular maintenance.
For many years now, Greener Waste Limited has been working on finding natural solutions to improving the reliability and performance of fixed film filters. The Bio-Selector bio-augmentation method, developed over a number of years of research, involves the use of carefully selected bacteria strains, which are grown and acclimatised in a side process on the sewage works. The strains of bacteria, chosen after careful laboratory tests, are pre-activated and dosed into the head of the works.
By bio-augmenting the treatment process in this way, improved up-front degradation of fats and greases in the primary function of the works can be achieved. Primary tanks are cleared of floating fats, dosing siphons do not block and the presence of fatty solids passing to the distribution arms and filter beds is removed. Bio-augmentation helps to improve the efficiency of the process equipment on site and has been proven over time with a number of utilities.
The efficient breakdown of fatty matter continues on the biological filters, removing surplus solids and allowing greater oxygen transfer across the media leading to improved BOD/COD removal with the added benefit of improved nitrification in the lower levels.
Exhaustive full- scale trials have been carried out with the cooperation of a number of utilities to prove the efficacy of the process and considerable data is available to support its viability.
As an example of how small works can benefit, a Bio-Selector 100 bio-augmentation unit was installed on a small coastal works with a DWF of 350 m3/day and which suffered from seasonal overloading as a result of an annual influx of caravans and holidaymakers to the local villages. The filter beds were heavily clogged with solids and were ponding badly before the season had started - a situation that occurred on an annual basis and which various unsuccessful attempts to cure had been made. A BioSelector 100 was installed and by bio-augmenting the site, the volume of solid matter tied up in the beds was reduced. The problem of ponding was eliminated within four weeks, the BOD and COD levels dropped, nitrification improved and the beds were able to handle the increased summer load successfully with the works remaining within consent. Continued use of the Bio-Selector will maintain site performance at its new level.
The bio-augmentation of the coastal biological filter site cost less than the capital cost required to manually clean and repair the filters. It has reduced the number of maintenance call outs and turned a borderline works into an efficient unit. The Bio-Selector technology applied by Greener Waste Limited requires attention from a service engineer only once per month and brings filter bed technology back into the 21st century as a simple, reliable, low manpower process in a carbon footprint and environmentally friendly way. The addition of the Bio-Selector bio-augmentation helps support the automation of small filter bed sites, whilst, most importantly, enabling the works to operate within the EA consent.