The food processing waste, sunflower seed shells (SS), were chemically modified and tested as adsorbents for nitrate removal from water and wastewater. Chemical modification of the SS implied a quaternization reaction. Efficiency and mechanisms of nitrate removal from water by modified sunflower seed shells (MSS) were examined using model nitrate solution (MS) and samples of real wastewater (RW) in batch adsorption experiments while the regeneration capacity was tested by fixed bed adsorption column and regeneration experiments. The MSS had the highest nitrate adsorption capacity of 12.98 mg g⁻¹ for model nitrate solution, 12.16 mg g⁻¹ for model wastewater, 13.70 mg g⁻¹ for the wastewater generated by the confectionery industry (CI), and 12.52 mg g⁻¹ for the wastewater generated from the meat industry (MI). Equilibrium data were analyzed, and results demonstrated a better fit for the Freundlich isotherm model, while kinetic models showed that the adsorption has pseudo-second-order kinetics. Adsorption and desorption experiments in fixed bed columns showed good MSS regeneration performances and efficiency after a minimum of three cycles. Lower efficiencies of regenerated MSS were noted when real confectionery and meat industry effluent were treated. Environmental toxicity of nitrate saturated MSS was tested using an acute toxicity test with freshwater plankton Daphnia magna. SS showed very good properties and could be competitive among already known and existing “low-cost” adsorbents as potential adsorbents for nitrate removal from water and wastewater.

Although the coking industry is a major polluter, it is still an important and irreplaceable industry in many countries. Wastewater from the coking industry typically contains large amounts of various hazardous substances, including phenols, cyanides, and thiocyanates; we conducted a comprehensive study on their ecotoxicity. This included five different toxicity tests with common species from different trophic levels: the bacteria Aliivibrio fischeri and Pseudomonas putida, the microalgae Chlorella sp., the duckweed Lemna minor, and the onion plant Allium cepa. These tests have rarely or never been used for these three toxicants. The results show that cyanide generally has the highest toxicity, while phenol has a relatively equal or higher toxicity than thiocyanate, depending on the test. Since no data on the joint toxic action of these three toxicants can be found in the literature, and although their joint occurrence in the aquatic environment is very likely, we performed joint toxic action analysis. The analysis was performed for binary and ternary mixtures of the toxicants using the Aliivibrio fischeri test. The concentration addition model was used as a reference model for the toxic behavior of these mixtures. The results obtained showed a synergistic deviation from the concentration addition model for combinations of phenol with cyanide and with thiocyanate, while the combination of cyanide and thiocyanate led to additive toxic behavior.