As a result of increasing population, industrialization, and effluent quality, sludge production has increased worldwide. Organic micropollutants in sludge have become a more critical environmental health concern compared to heavy metals. New sludge disposal regulations limit persistent organic pollutants (POPs) in addition to conventional organic indicators like total and dissolved organic carbon. This study aims at providing a brief review on POP concentration in the sludge in different regions of the world, sludge regulations, assessment of conventional biological sludge stabilization methods according to their ability to remove POPs, and discussions on alternative sludge treatment methods. The impact of sludge treatment unit operations including conditioning, thickening, mechanical and thermal dewatering, and biological and thermal stabilization on sludge management is also discussed in the context of organics. The occurrence and removal of micropollutants such as absorbable organic halogen compounds (AOX), nonylphenol and nonylphenol ethoxylates (NPE), di-2-(ethyl-hexyl)-phthalate (DEHP), dibenzo-p-dioxins and furans (PCDD/F), polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) are also evaluated specifically for sludge treatment unit operations. A concise discussion is also included on different drying technologies suitable for drying of sludge.

The removal of Acid Red 114 (AR114) dye by adsorption process, using the magnetic nanoparticle (RHA-MNP) which is produced from rice husk ash burned at 300°C and the magnetic nanoparticle (MNP, Fe₃O₄), was studied. Batch processes were used under different test parameters: pH (2, 4, 6, and 10) and without pH, initial dye concentration (20, 40, 60, 80, and 100 mg/L), and contact time (0, 1, 5, 10, 15, 30, 45, 60, 90, and 150 min). Optimum conditions for AR114 removal were found to be at natural pH (pH without correction) for both adsorbents. Freundlich isotherm was found to be more consistent for MNP and Langmuir isotherm was found to be more consistent for RHA-MNP. The maximum adsorption capacities of MNP and RHA-MNP adsorbents for AR114 dye were equal to 111 mg/g. The kinetic experimental data fitted the pseudo-second-order model for both MNP and RHA-MNP. It can be concluded that RHA-MNP which is a waste could be used as low-cost adsorbent to remove AR114 from aqueous solution.

A wide range of products are produced in the chemical producing industry such as textile dyes, chemicals, printing dyes and chemicals, paper chemicals, electrostatic powder dyes, and optical brighteners. The aim of this study is to investigate the treatability of chemical oxygen demand (COD), aromaticity, and color in the wastewater of this sector, where highly complex chemicals are used. Most of the studies in the literature are related to the treatment of synthetically prepared dyed wastewater. This study is important as it is carried out with real wastewater and gives results of many treatment methods. In the study, COD, UV-vis absorbance, and color values were attempted to be removed from the wastewater of a chemical producing industry that was pretreated by coagulation-flocculation. The COD value of the pretreated wastewater discharged to the central treatment system was restricted as 1000 mg/L. Pretreated wastewater characterization is as follows: COD: 2117 mg/L, UV-vis absorbance values at; 254 nm: 9.91, 280 nm: 8.65, 341 nm: 12.77, 436 nm: 5.01, 525 nm: 2.24, and 620 nm: 1.59. In the study, adsorption, ozonation, and advanced oxidation processes (Fenton and persulfate oxidation) were used to remove COD and UV-vis absorbance values (aromaticity, organics, and color). The method by which the best removal efficiency was obtained for all parameters was the adsorption process using powdered activated carbon (PAC). The equilibrium PAC dose was found as 6 g/L. At this adsorbent dose, the removal efficiencies of UV-vis absorbance values were all around 99% and the efficiency of COD removal was 77%. The Langmuir isotherm constants were found to be qmax= 30.4 mg/g and KL = 487.9 (L/mg). The COD concentration at this adsorbent dose was 486 mg/L and wastewater was suitable for discharge to the central wastewater treatment plant in that region.

The objective of this study is to evaluate the performance of H₂SO₄− activated rice husk ash (ARHA) (burned at different temperatures (300–550°C) as compared to granular activated carbon (GAC) in the removal of methylene blue (MB) from aqueous solution. Batch studies were performed to evaluate the influences of various experimental parameters like pH (4, 7, 9, and 11), initial concentration (5, 10, 15, 20, 25, and 50 mg/L), and contact time (0, 1, 5, 15, 30, 45, 60, 90, and 120 min). BET surface areas for ARHA300 (burned at 300°C) and ARHA550 (burned at 550°C) were determined as 143 and 68 m²/g, respectively. It was observed that the dye uptake by GAC and ARHA300 were not changed significantly when the pH of dye solution was increased from 4 to 11. Uptakes of dye were rapid and the adsorption increased with increasing contact time in all experiments. According to the R² values for the adsorption of MB on ARHA300, ARHA500, and GAC, Langmuir model yields fit better than the Freundlich model. The maximum adsorption capacity, q_max of ARHA300 (44.25 mg/g), had the highest value. The pseudo-second-order kinetic model yields the best fit for adsorption on ARHA300 and ARHA550 and the correlation coefficients R² of the model for the linear plots are very close to 1 at various concentrations.

The present study aims to explore the characterization of industrial container and drum cleaning (ICDC) industry wastewater and treatment alternatives of this wastewater using Fenton and adsorption processes. Wastewater derived from ICDC industry is usually treated by chemical coagulation and biological treatment in Turkey and then discharged in a centralized wastewater treatment facility. It is required that the wastewater COD is below 1500 mg/L to treat in a centralized wastewater treatment facility. The wastewater samples were characterized for parameters of pH, conductivity, COD, BOD₅, TSS, NH₃-N, TN, TOC, TP, Cd, Cr, Cu, Fe, Ni, Pb, Zn, and Hg. Initial COD values were in the range of 11,300–14,200 mg/L. The optimum conditions for Fenton treatment were 35–40 g/L for H₂O₂, 2–5 g/L for Fe²⁺, and 13–36 for H₂O₂/Fe²⁺ molar ratio. The optimum conditions of PAC doses and contact times in adsorption studies were 20–30 g/L and 5–12 h, respectively. Removal efficiencies of characterized parameters for the three samples were compared for both Fenton and adsorption processes under optimum conditions. The results suggest that these wastewaters are suitable for discharge to a centralized wastewater treatment plant.