Why RAS? Isn't it expensive and complicated? No, and here's why.
The fundamental capability of any RAS is the water conditioning and treatment methodology selected for use. Holder Timmons Engineering (HTE) generally designs the RAS to include a proprietary floating microbead filter developed by the engineering staff of HTE. We refer to this biofilter as the HTE Biofilter™.
Floating bead biofilters are based upon publicly available information and research data, but HTE has developed and incorporated proprietary design and water management features that makes the HTE Biofilter™ unique and which provide significant initial and life cycle economic benefit to the operator. All floating microbead filters have the following advantages (as described by Greiner and Timmons 1998 ) in comparison to other filter technology:
* low hydraulic head requirements to operate, e.g. approximately 1.5 m of lift above the height of the fish column water (or less).
* very low operating cost due to the use of low-head pumps as allowed by Feature #1
* low impact of loss of media from the reactor, as compared to fluidized sand beds. Floating microbeads, no larger than 4 mm in diameter, are readily available and are very low cost, e.g. $2.00 per cubic foot delivered.
Diagram of the HTE-Biofilter™
This device offers considerable and demonstrable advantages over all other currently available filtration systems. The HTE Biofilter™ combines processes for CO2 stripping, oxygen addition, nitrification, and fine solids capture into a single unit in a synergistic and unprecedented fashion. This combination of what was heretofore several individual processes into a single unit device results in significant economy of scale and system design simplicity. The HTE Biofilter™ is simple to operate since it is essentially a trickling filter using microbeads (1 to 4 mm diameter polystyrene balls with a bulk density of 1 lb/ft3) for media. A significant cost benefit of the HTE Biofilter™ is that it can be designed to supplement all or part of the barn's ventilation system. This unique feature will save construction and equipment costs in a new facility, and can reduce utility operating costs significantly in a facility retrofit to replace obsolete filtration technology with the HTE Biofilter™. It also provides the additional benefit of improving the building's air quality and increasing the level of human comfort. This capability has a noticeable cost-avoidance advantage, in that construction and operational costs for a separate ventilation system can be reduced or perhaps eliminated entirely. Additionally, the HTE Biofilter™ will greatly enhance the aerial environment within the building, leading to greater human comfort.
The HTE Biofilter™ operates on minimal hydraulic head pressure that allows the use of high volume - low head pumps that are economical to operate, thus reducing production costs. The combination of virtually all the water treatment requirements into a single unit reduces floor space requirements for this equipment, resulting in either more space for production or a smaller overall facility, thereby making the overall initial costs of an indoor aquaculture system proportionately less expensive.
A cost comparison of various filtration and conditioning alternatives indicates the relative economic advantage of the HTE Biofilter™. Previous micro-bead filters as described by Greiner and Timmons (1998) were restricted to biofilters that were capable of assimilating only around 1 kg TAN per day (or roughly 1 cubic meter of biomedia). Even though the microbead filters have been used for several years quite successfully, they were limited in their size due to the fluidization characteristics of the beads. Attempts at making larger units to take advantage of the scale effect were unsuccessful due to the high buoyancy of the microbeads which caused the filter to "short circuit" the flows resulting in lack of capacity, as production capacity had to be sized to the constraints of filter performance. Proprietary information developed by HTE allows the HTE Biofilter™ to be scaled to any size.
