FISH FARMING TECHNOLOGY
#1
Aeration with Ceramic Micro Bubble Diffusers By Dietmar Firzlaff, aquaFUTURE, USA
One of the oldest technologies known to mankind is the use of ceramics. For around 25,000 years ceramic clay materials have been taken from the earth, shaped, fired and used by humans for purposes of making pottery for storing food and water, ovens for cooking and melting metals to fashion into tools and weapons. Ceramic technology has advanced significantly over the past few decades.
The development of high temperature ceramics for space shuttle tiles, electrical insulators, bullet proof vests, artificial hip joints and superconductors for electronics all have made great impacts in advancing civilisation’s overall technology. Unfortunately, very little has been done in the past 30 years to improve traditional ceramic micro bubble diffusers for aquaculture. Since the invention of a mechanical air pump in 1908 that opened the doors for the beneficial aeration in aquatic systems, traditional air stones were invented. These have been fashioned from limewood or porous stones. Although fish farming has advanced in recent years and the most common methods used for aeration have been proven to be energy intensive (paddle wheels) or inefficient due to the formation of large bubbles as shown by porous hoses or even membrane diffusers, the costs of this equipment soon outweigh the long-term operational costs of wasted electricity and oxygen. These methods of aeration are unfortunately still popular and available due to misleading advertisements, insufficient infrastructure and possible lack of finance to upgrade to a modern practical technique. In the 1980s, with advances in industrial porous ceramics for water filtration and catalysts, micro bubble diffusers were developed to address the need for more efficient and reliable aeration in fish farming. Fish stocking capacity is primarily limited by oxygen availability and therefore needs a reliable system to boost oxygen levels. These newly developed rectangular ceramic diffusers have traditionally been used in intensive fish farming to aerate water effectively during the transporting of fish, as a backup system when there is a pump or power failure, or simply to increase Dissolved Oxygen (DO) levels when required: e.g. during feeding or weather heat spells when fish require more oxygen and DO levels drop. This new type of ceramic diffuser showed, in comparison to other methods of aeration, a very efficient way of increasing DO levels, but they lacked durability. Ceramics are very rigid and are therefore prone to breaking from over pressurising or accidental dropping during handling. Ceramic pores tend to clog up with algae growth over time thus decreasing performance. In addition, these diffusers show failure due to corrosion of the aluminium base and brass fittings, still being used to date to house the ceramic membrane for some popular diffusers designed over 30 years ago. Unfortunately, over the past few years, some major brands of diffuser have given ceramics a bad reputation in the aquaculture industry. The quality of one brand deteriorated significantly since it outsourced its manufacturing. Another major brand, a cheaper version marketed by many corporate equipment suppliers, tends to break spontaneously. This has resulted in some fish farmers choosing alternative, somewhat controversial oxygenation methods. Enviro Ceramic Diffusers were developed with a long lifespan and aeration efficiency in mind. In addition, it challenges the design of simple rectangular ceramic diffusers. Since 2010, Enviro Ceramic has continually studied and identified the key features required to optimise the efficiency of diffusers and addressed some of the main causes of failure during use.
Optimising Efficiency
Efficiency means reducing losses. Losses for diffusers are measured in oxygen consumption vs. maintaining safe DO levels for the fish and this is all measured in relation to energy costs. Diffuser performance optimisation can be achieved by tweaking the ceramic to produce the smallest possible bubbles and its overall design features. These include: the smaller the bubble generated, the higher its capability for gas absorption into the water, efficiently increasing the DO levels. The bubble size depends mainly on the ceramic pore sizes, the number of pores per given area and their distribution over its surface and also on the surface tension between the ceramic surface and water interface. 38 | July 2018 - International Aquafeed