Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2000-12-14
2003-06-03
Prince, Fred (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S747300, C210S170050, C047S001400
Reexamination Certificate
active
06572770
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus and method for harvesting and collecting aquatic plant biomass, and more particularly, to a system and method for harvesting and collecting attached algal communities or algal turf whereby water is utilized to transport algal biomass to a central collection location.
2. Description of the Background Art
For over one hundred years, government agencies and private entities have been attempting to design and develop strategies for harvesting aquatic plants. Initially, research efforts were directed at removal of aquatic plants from open water systems. Then, during the mid nineteen seventies, as researchers began to investigate the use of aquatic plants in water treatment, investigation began into harvest systems for use in man-made treatment systems.
In natural open water systems, the need to harvest aquatic plants is driven largely by the need to remove nuisance vegetation with capture of nutrient pollutants bound into plant tissue largely a secondary consideration. In constructed water treatment systems, harvesting of aquatic plants is necessary not only to gather plant biomass as a “crop” but also to remove plant tissue and attendant nutrient pollutants and maintain the overall health of the system.
Requisite to the function of many constructed water treatment systems is the cultivation of aquatic plants such as water hyacinth, duckweed or attached algal communities. The concept of artificial algae systems or Algal Turf Scrubbers (hereinafter “ATS”) was first developed to permit nutrient management within aquaria-type facilities in which organisms, such as reef corals, which rely upon very low nutrient levels, could be sustained and cultivated. An ATS consists of a natural, mixed assemblage of attached periphyton, microalgae and bacteria which colonise a water floway, usually inclined, over which wastewater or nutrient rich water flows.
ATS are cultured communities of attached or benthic algae that can be used to manage water quality or to scrub a variety of nutrients or contaminants from marine, estuarine, and fresh water. ATS are complex algal communities and, as such, do not demonstrate the sensitivities and instabilities characteristic of monocultures of algae. See Adey, W. H., C. Luckett, and K. Jensen. 1993. “Phosphorus removal from natural waters using controlled algal production”.
Restoration Ecology.
March 1993: 29-39.
It was discovered that when accompanied by extensive natural energies, such as currents or wave oscillations, algal communities within an ATS could sustain significant levels of productivity. Subsequently, it was suggested that algal communities could be supported within an engineered system to reduce nutrients, particularly phosphorus, from large volumes of nutrient enriched surface waters, such as wastewater and non-point sources (NPS). Today, ATS systems are used in thousands of aquaria, including a number of large-scale cultivation units (up to 1 million gallons). Studies in maximizing production of algal communities or “algal turf” and its uses continue and are well-known and reported in patents and literature. By way of background, see U.S. Pat. No. 4,333,263 to Adey; U.S. Pat. No. 4,966,096 to Adey; U.S. Pat. No. 5,097,795 to Adey; U.S. Pat. No. 5,778,823 to Adey; U.S. Pat. No. 5,851,398 to Adey; and U.S. Pat. No. 5,715,774 to Adey et al. It should be noted that the foregoing: patents contemplate harvesting algal turf from its growth substrate by means of hand, livestock, fish or machinery. The disclosure and teaching of these patents are incorporated herein by reference in their entirety.
Recently, there has been an increase in aquatic plant based water treatment (“APBWT”) applications, primarily in the production of fish for human consumption and in nutrient based water treatment systems. Specifically, aquatic plant based water treatment is a mechanism to address non-point source (NPS) pollution such as nutrient pollutants. If the design and operation of constructed commercial sized aquaculture based facilities is to become economically viable, an improved mechanism to manage aquatic plant biomass is necessary.
The major challenges for water treatment technologies employing aquatic plant systems is accessing the plants, efficiently and economically harvesting and collecting the aquatic biomass, and efficiently and economically processing the harvested aquatic biomass.
Two critical items govern the potential value of the aquatic plant biomass generated from water treatment systems. The cost of production and the quality of the product produced. As the plant tissue of an aquatic plant is typically 95% moisture, the total weight of the wet plant tissue is significantly greater than that of terrestrial crops on an equivalent dry weight basis. Accordingly, handling strategies for harvested aquatic plant biomass are critical to the economic cost of handling the biomass.
Harvesting of algal biomass from an ATS, or biomass management, is critical to the sustained performance of an ATS. Harvesting of algal biomass from an ATS occurs on a regular basis, preferably every seven to twenty-one days. Therefore, it is of paramount importance that the biomass management be efficient and cost effective.
Prior art methods for harvesting aquatic plants in natural open waters systems have focused largely on self-propelled floating harvest devices. Severed or collected plant material is either left floating in the water, chopped and left floating in the water, transported to shore by barge or floating in bales, transported by helicopter, or chopped plant material may be pumped as a slurry to a land-based receiving station. Prior art methods for harvesting aquatic plants in natural open water systems have not been employed in the management of aquatic plants within constructed water treatment systems as the harvest strategies are expensive, thereby driving up the cost of the water treatment technology to unacceptable levels. Aquatic plant harvest strategies employed in constructed water treatment systems reflect continuing attempts to improve harvesting efficiency.
There presently exists several apparatus and methods to harvest algal communities. Early methods of harvesting ATS, usually in small scale installations, included hand harvesting which entailed simply scraping algae off the growth substrate. Specifically, the growth substrate or screens were harvested by physically removing the screen from the scrubber and placing it on an inclined easel. Biomass was removed from the screen by scraping with a moderately sharp implement such as piece of hard polystyrene plastic. Scraped biomass was collected in a strainer and de-watered. Difficulties with a hand scraping approach are two-fold. First, depending upon the size of the ATS, it may be difficult to access all portions of the algal turf. Secondly, harvesting via scraping often incompletely removes portions of the algae and allows dislodged algae fragments to settle within the ATS or otherwise not be collected. Incomplete collection of aquatic biomass may permit the release of nutrients which were taken up by the attached algal communities.
In order to expedite harvesting, approaches utilizing vacuum equipment have been utilized. On a small scale, variations of “shop vacs” have been utilized to vacuum biomass directly from the ATS growth substrate. For large-scale installations, heavy vacuum equipment designed to vacuum the floway has been utilized. A vacuum unit, either tractor pulled or self-propelled, is typically land based and gains right of entry to the ATS via an access road or floway. However, heavy vacuum equipment has significant operation costs when applied to a large scale ATS system.
Other algal turf harvest systems have included structured floways requiring perimeter wall or curbs employed for retaining water in the floway and facilitating movement of the harvest equipment that is too heavy to travel on the synthetic membrane lined ATS.
Continuing efforts are being made to improve ATS and harvesting of algal
Stewart, III E. Allen
Zivojnovich Mark J.
Holland & Knight LLP
Hydromentia, Inc.
Prince Fred
LandOfFree
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