Treatment and Recycle of Greenhouse Nutrient Feed Water Applying Hydrochar and Activated Carbon Followed by Reverse Osmosis

Abstract

Leached greenhouse nutrient feed (GNF) water is a great challenge for greenhouse (GH) producers. Unbalanced higher micronutrient metal’s phytotoxicity impact GH plant growth, and the high phosphorous levels can cause lake eutrophication if not treated. The analytical results of three GNFs revealed no microbial contamination in any of the GNFs, but the potassium, calcium, magnesium levels, and pH range were above the target level for root zone conditions. Both higher and lower limit concentrations are phytotoxic, causing poor or non-developed roots, leaves, and stems. Sodium was also not in the balanced range. Phosphate and nitrate nutrients were above the measurable range, showing that it would be a threat to lake eutrophication if disposed of. Due to uptake by plants at varied rates, nutrient ion imbalance in GNF is usual, but proper control or treatment is essential as GNF is not a waste but a resource providing fertilization to plants. Potential treatment options investigated include coagulation filtration, sorption with hydrochar (HC), and activated carbon (AC), followed by reverse osmosis (RO) membrane filtration. The HC and AC were produced from waste tomato plants biomass (TPB) of the same GHs to enhance the recycle–reuse of wastes. Neither metals nor nutrient concentrations were reduced to the desired levels by coagulation treatments. The HC and AC treatment provided the recycle–reuse possibility of GNF. RO membrane filtration provided about 97–99% reduction of metals and 99% reduction of nutrients, allowing GNF preparation by adding new fertilizer to the RO permeate. In such a case, the RO reject needs to be reused as feed for TPB carbonization. Different options for GHs to manage TPB and GNF are provided. As RO is an energy-expensive process, an assessment of technical know-how to provide an energy economic process is demonstrated.