Enhanced Reverse Osmosis Concentrate Disposal and Nutrients Conversion to Microalgae Bioenergy with a Gradient-Fed Strategy

Abstract

Reverse osmosis concentrate (ROC) disposal with microalgae has attracted increasing interest because of its intrinsic advantages, like simultaneous wastewater remediation and bioenergy production. But these processes are currently suffering from inefficient nutrients removal and poor microalgae growth due to ROC toxicity. A gradient-fed strategy is proposed to enhance ROC disposal and nutrients conversion to microalgal Chlorella vulgaris lipid by adjusting the ROC feeding. Time-evolving profiles of nutrients and chemical oxygen demand (COD) during experiments as well as their influences on microalgae growth and metabolism have been investigated. Results indicate that the removal of NH4 + and COD using the gradient-fed process was improved by 104.3% and 214.2% compared to those obtained in batch mode, generating a high-quality ROC effluent with N and P nutrients almost totally removed. Microalgae biomass and lipid content were simultaneously enhanced with the gradient-fed process. Energy production analysis showed that the highest energy yield was achieved with use of the gradient-fed process at 30%–70%–100% as 39.0 kJ/L, which was higher than the volumetric heat value of natural gas (about 36.0 kJ/L) and significantly higher than that obtained in batch mode (21.6 kJ/L). This work provides a practical strategy for large-scale microalgae cultivation with ROC.

Sulfite activation by oxidized pyrite for dye degradation assisted by oxygen

“…RB decolorization enhanced initially with the dosage of OP increased from 0.10 to 0.50 g L À1 and then the decolorization decreased when the OP dosage further increased to 1.00 g L À1 . The result could be explained as that the increase of OP dosage could increase the iron content, which could provide more active sites 29 to produce more SO 4 À to remove…”

“…Because oxygen played an essential role in the formation of SO 4 À through eqn ( 5) and ( 6), the effect of DO on RB decolorization was examined by the OP/SS system with or without air/ N 2 purging. Fig.…”

“…Sulfate radical (SO 4 À )-based advanced oxidation processes (SR-AOPs) have attracted the attention from many researchers in the treatment of organic sewage due to their high redox potential (2.5-3.1 V) and efficacy, and great selectivity. 1,2 In most cases, SO 4 À is generated from peroxymonosulfate (PMS)…”

“…or peroxydisulfate (PDS) activation. 3,4 However, the residues of PMS and PDS are potentially harmful to human health and the environment in the reaction system after the pollutants are degraded because of their acute toxicity. 5,6 Therefore, the cheap and eco-friendly sulfite is newly regarded as a replacement of PMS and PDS, which can also derive SO 4 À under catalysis of transition metals.…”

A Study on The Carriers Compound Multi-Stage MBBR Biological Treatment Process for Domestic Sewage

“…Although deep treatment by physicochemical methods such as ozone oxidation or activated carbon treatment is extremely effective, there are problems of membrane contamination, high energy loss, high cost, and secondary contamination that limit the application of physicochemical methods, such as membrane contamination, high energy loss, high cost of drug addiction, and secondary contamination in the process. Although advanced treatment by physicochemical methods such as ozone oxidation or activated carbon treatment is more effective, biofilm-based treatment processes, such as moving bed biofilm reactor (MBBR) technology, may also be options to improve MP removal and they are heavily used in various wastewater treatment configurations [4].…”