Treatment of dye-containing wastewater using discarded animal blood-derived hemoglobin crystals

Ever-expanding industrial and agricultural production has satisfied human needs but unfortunately causes serious environmental pollution. Pollutants such as dye-containing wastewater from the dye industry and animal blood waste from the meat industry impose heavy burdens on the environment and are difficult to treat. Here we demonstrate that hemoglobin crystals prepared from animal blood waste can effectively and selectively adsorb and remove organic pollutants from dye-containing wastewater. This approach simultaneously mitigates two types of environmental pollutants: wastewater dye and animal waste. The absorption properties of low-cost and stable cross-linked hemoglobin crystals (CLHCs) prepared from discarded chicken blood were experimentally tested on various dyes (methylene blue, malachite green, methyl orange and Congo red). The CLHCs adsorbed all dyes in a pH-dependent manner, achieving controllable selective adsorption. Adsorption of anionic dyes was especially effective, with an adsorption capacity of 184.18 mg/g for methylene blue. Unexpectedly, the CLHCs also exhibited degradative activity against methylene blue and malachite green. Mechanistic studies showed that the crystals removed methylene blue mainly by multi-layer physical adsorption and malachite green mainly by chemical degradation. Finally, we evaluated whether CLHCs can remove dyes from actual wastewater to promote the germination of contaminated rice seeds. Our results confirm that hemoglobin crystals can effectively treat dye-containing wastewater in practical scenarios.