Packed-bed biofilm reactor for semi-continuous anaerobic digestion of olive mill wastewater: performances and COD mass balance analysis

Analysis of Chemical Oxygen Demand in Barrel Finishing Based on Reusing Water Resource of Grinding Fluid

To explore the sustainable development of grinding fluid in barrel finishing, the idea of water resource reuse in grinding fluid has been proposed. The influence of the graphene oxide (GO) and the sodium dodecyl benzene sulfonate (SDBS) as main components in the grinding fluid on the chemical oxygen demand (COD) was analyzed. Repreparing new grinding fluids by utilizing the water resources in grinding fluid after finishing will not cause a sharp increase in COD value. GO which absorbs SDBS can be taken away from grinding fluid by physical separation. It will decrease the COD value of grinding fluid. However, SDBS exists in the form of colloids in the grinding fluid and cannot be removed through physical separation, which also affects the COD value. Based on water quality indicators (the COD, pH, total hardness, metal aluminum, anionic surfactants, and total dissolved solids), the water quality index (WQI) of the reusing grinding fluid after finishing by the physical separation is significantly reduced. It indicates that reusing water resources in grinding fluid is a feasible way to reuse grinding fluid.

Efficiency of various biofilm carriers and microbial interactions with substrate in moving bed-biofilm reactor for environmental wastewater treatment

In a moving bed-biofilm reactor (MBBR), the fluidization efficiency, immobilization of microbial cells, and treatment efficiency are directly influenced by the shape and pores of biofilm carriers. Moreover, the efficacy of bioremediation mainly depends on their interaction interface with microbes and substrate. This review aims to comprehend the role of different carrier properties such as material shapes, pores, and surface area on bioremediation productivity. A porous biofilm carrier with surface ridges containing spherical pores sizes > 1 mm can be ideal for maximum efficacy. It provides diverse environments for cell cultures, develops uneven biofilms, and retains various cell sizes and biomass. Moreover, the thickness of biofilm and controlled scaling shows a significant impact on MBBR performance. Therefore, the effect of these parameters in MBBR is discussed detailed in this review, through which existing literature and technical strategies that focus on the surface area as the primary factor can be critically assessed.

CO2 sequestration mediated by wollastonite in anaerobic digestion of sewage sludge: From sequence batch to semi-continuous operation

This study investigated the mechanisms involved in CO₂ sequestration under the sequence batch and semi-continuous operation using wollastonite in sludge anaerobic digestion. Wollastonite substantially elevated CH₄ content in biogas and played a role in CO₂ capture. It increased biogas yield of the glucose due to pH buffering effect but did not increase that of the hydrolysate from thermal alkali pretreated sludge. Under the semi-continuous operation, wollastonite improved the CO₂ sequestration, but decreased the biogas yield from 166 to 24 mL/g soluble chemical oxygen demand, since seemingly wollastonite residues inhibited microbes in the sludge. However, the use of dialysis bags to wrap wollastonite offset the negative impact of the wollastonite residues in the sludge, thereby increased biogas yield. The present study is conducive to understanding the mechanisms involved in and proving the feasibility of the CO₂ sequestration using wollastonite in sludge anaerobic digestion and its impacts on long-term operation. Consequently, the findings of the study provide key parameters and useful guidelines for scaling up and wollastonite application in anaerobic digestion of sewage sludge.

Biochar for Wastewater Treatment—Conversion Technologies and Applications

Biochar as a stable carbon-rich material shows incredible potential to handle water/wastewater contaminants. Its application is gaining increasing interest due to the availability of feedstock, the simplicity of the preparation methods, and their enhanced physico-chemical properties. The efficacy of biochar to remove organic and inorganic pollutants depends on its surface area, pore size distribution, surface functional groups, and the size of the molecules to be removed, while the physical architecture and surface properties of biochar depend on the nature of feedstock and the preparation method/conditions. For instance, pyrolysis at high temperatures generally produces hydrophobic biochars with higher surface area and micropore volume, allowing it to be more suitable for organic contaminants sorption, whereas biochars produced at low temperatures own smaller pore size, lower surface area, and higher oxygen-containing functional groups and are more suitable to remove inorganic contaminants. In the field of water/wastewater treatment, biochar can have extensive application prospects. Biochar have been widely used as an additive/support media during anaerobic digestion and as filter media for the removal of suspended matter, heavy metals and pathogens. Biochar was also tested for its efficiency as a support-based catalyst for the degradation of dyes and recalcitrant contaminants. The current review discusses on the different methods for biochar production and provides an overview of current applications of biochar in wastewater treatment.

Biomethane recovery from olive mill residues through anaerobic digestion: A review of the state of the art technology

Residues from production of olive oil are generated yearly in great amounts, both in liquid and solid forms. Different waste treatment systems were proposed in literature, to minimize environmental pollution while raising the energy recovery. Anaerobic digestion is one of the available routes to recover energy from waste via production of biogas while reducing organic load and pollutants to the environment. The use of farming and agro industrial wastes as co-substrate in anaerobic digestion can induce benefits related to the simultaneous treatment of different wastes. In particular, co-digestion can significantly enhance the process stability as well as the bio-methane generation. This work aims at reviewing the latest achievements in anaerobic digestion of olive mill residues, focusing on the aspects that can mostly favor the process, principally from a technical but also from an economical point of view. For the mono-digestion processes, methane yields up to 419 L_CH4 kg_VS^-1 were reported for olive mill wastewaters (Calabrò et al. 2018), while a production of 740 L_CH4 kg_VS^-1 was achieved when digesting olive mill solid waste together with olive mill wastewater and milk whey (Battista et al. 2015). An increase up to 143% in the methane yield was also reported when the feedstock was subjected to a 5 days aeration before digesting it in a semi-continuous stirred tank reactor (González-González and Cuadros 2015).