Article written by: Jason Danaher Ph.D.
Aquaculture effluent contains organic fish waste, uneaten feed, suspended solids, and nutrient rich water with macronutrients and micronutrients that could benefit horticulture plants. Therefore, discharged aquaculture effluent has the potential to benefit integrated aquaculture systems if it can be captured and treated appropriately. There are many technologies and methods a farmer can use to convert discharged effluent into a user-friendly form for integrated systems. This article will briefly discuss geotextile technology and some of the benefits it may offer an operator.
A geotextile bag, or a geotube, is a permeable plastic fabric container designed to separate water from suspended solids (Figure 1). It is widely used in wastewater treatment, dredging, manure management, and increasingly in aquaculture to capture and treat discharged effluent from recirculating aquaculture systems. The process of treating the discharged effluent is relatively simple:
1) A polymer is injected into the untreated effluent before it enters the geotextile bag. The polymer causes the tiny, suspended particles to flocculate and clump together into larger particles which are more easily retained within the bag.
2) The geotextile fabric allows the water to escape while trapping the solids within the bag. It has been shown geotextile bags retain greater than 95% of the solids entering the container when used with the appropriate polymer. Over time, the water portion of the effluent that entered into the bag seeps out and the solids dewater.
3) The filling and dewatering process repeats itself until the geotextile bag is full of dewatered solids.
Figure 1. A geotextile bag dewatering discharged aquaculture effluent from a recirculating aquaculture system. The bag retains the majority of suspended solids and allows water to weep into a containment area for later use on a soil-based farm.
During each pumping event the operator produces a clarified water and a concentrated, nutrient rich biosolids. The water can be captured and applied to containerized plants or soil-based systems as a water and nutrient source without prematurely clogging traditional horticulture irrigation equipment. The solids can eventually be removed from the geotextile bag and either land applied, composted, or blended into growing media for greenhouse plant production.
As with any nutrient solution or growing media used in plant production it is important to control/monitor physical parameters (i.e. air space, water holding capacity, total porosity, bulk density) of the substrate when mixing in the dewatered aquaculture effluent and control/monitor chemical parameters (i.e. pH and electrical conductivity) of the water exiting the geotextile bag to ensure optimal ranges are met for plant production.
Feel free to call Aquatic Equipment & Design, Inc. staff at 407-995-6490 or email info@aquaticed.com for additional information on geotextile technology and its use for dewatering discharged effluent from your recirculating aquaculture system.