The sludge-based adsorbent from oily sludge and sawdust: preparation and optimization

Synergistic Preparation of Sludge Carbon from Oily Sludge and Walnut Shells

The preparation process of synergistic preparation of sludge carbon by oily sludge and walnut shells are divided into two stages: carbonization preparation of a carbon precursor and activation preparation of sludge carbon. The preparation conditions of the carbon precursor are 2.5:1 mass ratio of oily sludge and walnut shells, carbonization temperature is 450°C, and time is 2 h. There are some pores on the surface of the prepared carbon precursor, the heavy metal content of leachate does not exceed the standard, and the use process will not cause heavy metal pollution. Intensive research is carried out on factors affecting the preparation of sludge carbon by activation of the carbon precursor by the orthogonal experiment and single-factor experiment. The optimal activation conditions are determined by using ZnCl2 as an activator, mass ratio of the carbon precursor to ZnCl2 is 1:4, activation temperature is 800°C, heating rate is 15°C/min, and activation holding time is 1 h. The surface of sludge carbon is distributed with many pores, several layers of small pores can be seen deeply in the large holes, and pore size distribution is dominated by micropores and mesopores. BET Specific surface area, pore volume, average pore, and iodine value are 1772.69 m2/g, 1.98 cm3/g, 1.64 nm, and 1011.65 mg/g, respectively, which surpasses commercially available activated carbon comprehensively.

Evaluate the effectiveness technology for the treatment of oily wastewater

This work deals with the treatment of oily wastewater produced from the washing of oil-contaminated soil. Untreated oily wastewater contains toxic compounds that might be mutagenic or carcinogenic as total petroleum hydrocarbon (TPH) and heavy metals. Based on the water quality analysis, the tested samples contained a high concentration of TPH, chemical oxygen demand (COD) and turbidity with an average value of 67,500 mg/l, 48,240 mg/l and 176 (nephelometric turbidity unit, NTU), respectively. Several technologies were used, such as centrifuging, powdered activated carbon (PAC) and sawdust. The mean values of COD values for sawdust, centrifuging and PAC were 41,067, 25,600 and 13,133 mg/l, respectively. The present study indicated that the coagulation/flocculation processes were more efficient by using aluminium sulphate alum, while the preliminary conclusion derived was that the secondary treatment using an aeration system is capable of lowering the COD values as well as increasing the flocculent mass floc well equal to 4,784 mg/l and 0.69 g, respectively. The microbial seed was able to degrade the biosurfactant, which allows the stability of oil emulsion to be broken down and released easily.

Recent Progress in Sludge Co-Pyrolysis Technology

With the development of society and industry, the treatment and disposal of sludge have become a challenge for environmental protection. Co-pyrolysis is considered a sustainable technology to optimize the pyrolysis process and improve the quality and performance of pyrolysis products. Researchers have investigated the sludge co-pyrolysis process of sludge with other wastes, such as biomass, coal, and domestic waste, in laboratories. Co-pyrolysis technology has reduced pyrolysis energy consumption and improved the range and quality of pyrolysis product applications. In this paper, the various types of sludge and the factors influencing co-pyrolysis technology have been classified and summarized. Simultaneously, some reported studies have been conducted to investigate the co-pyrolysis characteristics of sludge with other wastes, such as biomass, coal, and domestic waste. In addition, the research on and development of sludge co-pyrolysis are expected to provide theoretical support for the development of sludge co-pyrolysis technology. However, the technological maturity of sludge pyrolysis and co-pyrolysis is far and needs further study to achieve industrial applications.

Effects of Different Heat Treatment Methods on Organic Pollutants and Heavy Metal Content in Oil Sludge Waste and Ecotoxicological Evaluation

The discharge of large amounts of oily sludge heat treatment residues constitutes a severe threat to the environment. However, little is known about the toxicity of these heat-treated residues. Current research has mainly focused on the toxic effects of single heavy metals or single hydrocarbons on plants, whereas the phytotoxic effects of hydrocarbon–metal mixtures have remained largely unexplored. In this study, pot experiments were conducted to evaluate the effects of different proportions of heat treatment residues (pyrolysis, heat-washing, and high-temperature oxidation residues) from three kinds of oily sludge on the physiological and biochemical parameters of mung bean plants. Higher proportions of residues decreased the germination rates and enzyme activity of mung beans compared to uncontaminated soil. When pyrolysis residue, hot-washing residue, and high-temperature thermal oxidation residue are used in green planting soil, their content must be lower than 30%, 90%, and 70%, respectively. Additionally, our findings indicated that the accumulation level of pollutants in oily sludge heat treatment residues was not high. However, the three kinds of residues exhibited different degrees of plant toxicity. The pyrolysis residue still exhibited strong ecotoxicity, even at low concentrations. In contrast, the toxicity of the hot-washing residue was much lower than that of the pyrolysis residue and the high-temperature thermal oxidation residue. Our findings indicated that mung bean is highly tolerant of contaminated soil and is therefore well suited for phytoremediation applications.

Hierarchical Porous Catalytic Pyrolysis Char Derived from Oily Sludge for Enhanced Adsorption

A novel pyrolysis char (PC), prepared by H3PO4 catalytic pyrolysis of oily sludge (OS), was presented to remove methylene blue (MB) dye from aqueous solution for the first time. The optimal preparation conditions (catalytic pyrolysis temperature of 411 °C, H3PO4 impregnation ratio of 2.44, and catalytic pyrolysis time of 59 min) were predicted by the response surface methodology. The optimal PC exhibited favorable hierarchical porous properties, which brought a large adsorption capability (322.89 mg/g). The adsorption process fitted well with the Langmuir model and pseudo-second order model. In addition, thermodynamic parameters showed that the adsorption process was endothermic (ΔH 0 > 0) and spontaneous (ΔG 0 < 0). The adsorption capability was strongly influenced by coexisting metal ions due to the competitive adsorption effect. The inhibition for MB adsorption was arranged in the following order: Al3+ > Fe3+ > Mg2+ > Ca2+ > K+ > Na+. The adsorption mechanism of MB onto the OS-derived PC includes pore filling, π-π interactions, and electrostatic interactions. The as-obtained PC adsorbent exhibited good reusability performance, which leads to great potential in practical application for wastewater treatment.