Water and Effluent Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/831969
16 WET NEWS JUNE 2017 Bio-fouling can seriously affect pump capacity, water quality and borehole service life. Untreated, it will gradually clog and plug equipment with slime, scale and encrustrations, adversely affecting water colour, taste and odour. I-GONs let bio-fouling be bygones INSIGHT Valves, drives & actuators U nder-performance of a borehole can be extremely disruptive and have economic impacts for people and businesses that rely on them whether for irrigation, farming, ground heat extraction, dewatering, domestic use or potable water supply. Poor yield from a water well or borehole can happen for a number of reasons. These include inadequate well design, faulty or underspecified pumps and equipment, poor installation, dewatering or other aquifer issues, or system slowing and degradation from silting, corrosion and clogging. One of the most prevalent causes is the naturally occurring process of bio-fouling – the build-up of iron or manganese related bacteria which can seriously affect pump capacity, water quality and borehole service life. Bio-fouling manifests itself in the growth of bio-mass, the accumulation of living and dead bacteria which creates slime deposits within and around the borehole. The biomass blocks fissures, screens and pump intakes and pipes as it becomes established within the well. Water quality is affected; it may turn a tell-tale reddish-brown, o-en accompanied by an unpleasant taste and odour. Pump output slows, capacity is lost and the well could even become beyond rehabilitation, necessitating complete replacement. Bacteria The aggregation of the bio-mass initially acts as a natural biological filter, improving the quality of the water entering the borehole by removing iron and other metals along with organics. But as it grows, there is typically a reduction in the specific capacity of the borehole and the chemistry of the water changes. Bio-fouling may affect part or most of the borehole installation, and could lie deep within the system. Hazardous levels of bacteria may also be forming without any obvious indications at the surface. The bacteria are protected by biofilm which can slowly release the bacteria causing water contamination and potential health risks in drinking water wells. Maintenance intervention is generally recommended before the loss in borehole performance reaches 25%. There are a range of modern treatments for the removal of bio-fouling, depending on the severity of the infestation. Many of today's proprietary acid based treatments are generally designed for easy administering by the customer and are environmentally safe when correctly used. Where a more aggressive clean is required, chemical treatment may need to be supplemented by mechanical cleaning, such as jetting, scraping or wire brushing. In the case of severe fouling, stripping with a mineral acid, typically hydrochloric acid, may be necessary together with mechanical surging using surge blocks or jetting tools to increase surface contact. The disadvantage of hydrochloric acid is that it is highly corrosive, and can emit dangerous gasses when used. Shock chlorination is another option using chlorine based disinfectants, but these do not penetrate deep into the biofilm unless used in conjunction with strong mechanical agitation to facilitate increased surface contact. Ultimately, flagging output or downtime from a borehole has cost and operational impacts for the customer. The challenge is to develop treatments that are faster acting and more powerful, yet also safe and economic to administer while being environmentally sound. Economics The availability of more user friendly, added value treatments could also encourage the adoption of more frequent and effective preventative maintenance regimes that will see the best cost returns over borehole service life. In terms of the economics, a sound and systematic approach to maintenance can be around 10% of the cost of calling in a rehabilitation specialist. Effective, regular cleaning to keep bio-fouling at bay will avoid the potential catastrophe and significant costs of leaving a borehole to clog beyond recovery and require replacement. Proquip's I-GON treatment, an acid-based crystalline agent, has long been tried and trusted by the borehole industry for removing the iron and manganese oxides that lead to bacterial infestation and bio-fouling. Following months of development and trials, Proquip Direct has introduced a reformulated range I-GON2 and I-GON3 offering even quicker, more powerful yet still cost- effective cleaning. The new formula uses the proven and safe organic chemicals of the original, making it suitable for the treatment of potable water wells. But intensive work by an accredited water chemistry laboratory has led to exciting improvements in the physical characteristics to maximise cleaning reactions through the process. New I-GON uses grades of chemical that differ to •