Sustainable Alternatives for Tertiary Treatment of Pulp and Paper Wastewater

Determination of carbohydrate content in kenaf degumming wastewater and converting them to carbon dots

The traditional textile degumming process produces abundant wastewater, which contains a lot of monosaccharides and oligosaccharides. It is of great economic and environmental significance to utilize these carbohydrates in high value. In this study, high performance liquid chromatography (HPLC) was used to analyze the carbohydrate components in kenaf degumming wastewater, and then the production of C-dots using the wastewater was explored. The results showed that the types and content in the degumming wastewater were monosaccharides (glucose, xylose and arabinose) and oligosaccharides (dextran, xylan and araban). The carbohydrate (mainly glucan and xylan) content in wastewater accounted for 91.16 % of the total carbohydrates weight loss in kenaf degumming process. By using hydrolysis and hydrothermal reaction on kenaf degumming wastewater, blue-green carbon dots (C-dots) with good performance were prepared and successfully applied to anti-counterfeiting printing. In particular, the as-prepared C-dots prepared from kenaf degumming wastewater with urea added (WUC-dots) showed an excitation-dependent photoluminescence (PL) spectrum and quantum yield (QY) of 2.4 % in aqueous solution. The fluorescent code exhibited a clear outline, excitation-tunable color and good stability, showing a great potential for anti-counterfeiting system.

Green industry work: production of FeCl3 from iron and steel industry waste (mill scale) and its use in wastewater treatment

Mill scale (MS) is considered to be a significant metallurgical waste, but there is no economical method yet to utilize its metal content. In this study, which covers various processes in several stages, the solution of iron in MS, which is the Iron and Steel Industry (I&SI) waste, as FeCl3 (MS-FeCl3) in the thermoreactor in the presence of HCl, was investigated. In the next step, the conditions for using this solution as a coagulant in the treatment of I&SI wastewater were investigated using the jar test. The results of the treated water sample were compared by chemical oxygen demand (COD), total suspended solids (TSS), color, and turbidity analyses using commercial aluminum sulfate (Al2(SO4)3) and FeCl3 (C-FeCl3). Additionally, heavy metal analyses were conducted, and the treatment performance of three coagulants was presented. Accordingly, while 2.0 mg/L anionic polyelectrolyte was consumed at a dosage of 4.05 mg/L Al2(SO4)3 at pH 7.0, 0.25 mg/L anionic polyelectrolyte was consumed at a dosage of 1.29 mg/L at pH 5.0 in the C-FeCl3 and MS-FeCl3 studies. Also, Fe, Cr, Mn, Ni, Zn, Cd, Hg, and Pb removal efficiencies were over 93.56% for all three coagulant usage cases. The results showed that the wastewater treatment performance of MS-FeCl3 by the recycling of MS, which is an I&SI waste, was at the same level as C-FeCl3. Thus, thanks to recycling, waste scale can be used as an alternative to commercial products for green production.

How to choose the best tertiary treatment for pulp and paper wastewater? Life cycle assessment and economic analysis as guidance tools

Pulp and paper wastewater (P&P WW) often requires tertiary treatment to remove refractory compounds not eliminated by conventional biological treatment, ensuring compliance with high-quality effluent discharge or reuse standards. This study employs a life cycle assessment (LCA) methodology to compare alternative tertiary treatment technologies for P&P WW and rank them accordingly. The evaluated technologies in the scenarios include inorganic (S1) and organic (S2) coagulation-flocculation, ozonation (O3) (S3), O3+granular activated carbon (GAC) (S4), and ultrafiltration (UF)+reverse osmosis (RO) (S5). The analysis focuses on a P&P wastewater treatment plant (WWTP) in Northeastern Italy. The LCA is complemented by an economic analysis considering each technology's capital and operating costs, as well as potential revenues from internal effluent reuse. Results indicate that S4 (O3+GAC) outranks all the other scenarios in terms of both environmental performance and economic viability, primarily due to the advantages associated with effluent reuse. S5 (UF+RO), which also involves reuse, is limited by the high energy consumption of UF+RO, resulting in increased environmental impacts and costs. The physicochemical scenario S2 (Chem Or), currently utilized in the WWTP under study, remains the best-performing technology in the absence of effluent reuse. In contrast, S3 (O3 alone) exhibits the poorest environmental and economic outcomes due to substantial energy requirements for O3 generation and the inability to reuse the treated effluent directly. Lastly, a sensitivity analysis underscores the strong influence of chemical dosages in S1 and S2 on environmental and economic impacts, which is more significant than the impact of water reuse percentages in S4 and S5. The high electricity cost observed during 2022 negatively affects the energy-intensive scenarios (S3-S5), making coagulation-flocculation (S1-S2) even more convenient.