Assessing inorganic components of cake layer in A/O membrane bioreactor for physical-chemical treated tannery effluent

Stratified structure of membrane clogs observed in full scale cross-flow tubular ultrafiltration (UF) system: Fouling characterization and a proposed two-stage formation mechanism

Membrane fouling remains a significant challenge in wastewater treatment, hindering both efficiency and lifespan. This study reports a distinct phenomenon of stratified membrane clogging observed in a full-scale cross-flow tubular ultrafiltration (UF) system treating sludge anaerobic digestion (AD) reject water. The distinct stratified structure, comprising inner and outer layers within the cake layer, has not been previously described. This research involved characterizing the filtration performance, analyzing membrane clog composition, and proposing a two-stage formation mechanism for the stratified clogs. It was revealed that higher inorganic and lower organic content in the outer layer compared to the inner layer. Acid and alkali treatments demonstrated the effectiveness of combined cleaning strategies. A mathematical model was developed to determine the critical conditions for stratified clog formation, influenced by membrane flux and cross-flow velocity (CFV). It is proposed that outer layer forms through long-term selective deposition, while the inner layer results from short-term dewatering within limited tubular space. High CFV (>2.5 m/s) prevents inner layer formation. Critical conditions for stratification occur at a flux of 18 L/m2/h with a CFV of 0.1 m/s or 65 L/m2/h with a CFV of 0.35 m/s. This study contributes a novel understanding of stratified membrane clogging, proposing a two-stage formation mechanism and identifying critical conditions, which provides insights for effective fouling control strategies and maintenance of operational efficiency for membrane systems.

Efficient low-concentration phosphate removal from sub-healthy surface water by adsorbent prepared based on functional complementary strategy

The remediation of low-concentration phosphorus polluted surface water (LP-SW) is one of most challenging environmental issues worldwide. Adsorption is more suitable for LP-SW remediation due to its low cost and operability. Based on the strategy of functional complementation among industrial solid wastes (ISWs), ISW-based phosphate absorbent material (PAM) was prepared from coal ash (CA, binder), rich‑calcium (Ca) carbide slag (CS, active component) and iron salt (functional reagent) by optimizing materials ratios and roasting conditions. PAM prepared under optimal conditions (Fe/CC-2opt) had good phosphate adsorption efficiency. Notably, Fe/CC-2opt not only ensured that the effluent met Environmental Quality Standards for Surface Water (pH = 6.0-9.0), but also facilitated the formation of brushite instead of hydroxyapatite due to FeSO4 addition. Compared with hydroxyapatite, brushite had greater potential application value as fertilizer due to its solubility and high P/Ca ratio. The possible mechanisms of phosphate adsorption by PAM included surface precipitation, surface complexation, electrostatic adsorption and release of Ca2+/OH-. Preparation cost of PAM was 80 US$/ton, and treatment cost was 0.07 US$/g P. Regeneration efficiency of PAM was still above 80 % after five cycles. The design idea and result of this study provide theoretical basis and technical support for the preparation of PAM with low cost, commercial production and great adsorption capacity.

Effect of low molecular weight organic acids on the lead and chromium release from widely-used lead chromate pigments under sunlight irradiation

Lead chromate pigments are commonly used yellow inorganic pigments. They can pose environmental risks as they contain toxic heavy metals lead and chromium. Low molecular weight organic acids (LMWOAs), as widespread dissolved organic matter (DOM), affect the lead and chromium release from the pigment in water. In this work, the role of LMWOAs in the photodissolution of commercial lead chromate pigment was investigated. The pigment underwent significant photodissolution under simulated sunlight exposure with LMWOAs, and subsequently released Cr(III) and Pb(II). The photodissolution process is caused by the reduction of Cr(VI) by photogenerated electrons of the lead chromate pigment. The LMWOAs promoted photodissolution of the pigment by improving the electron-hole separation. The formation of Cr(III)-contained compounds leads to a slower release of chromium than lead. The photodissolution kinetics increase with decreasing pH and increasing LMWOAs concentration. The photodissolution of lead chromate pigment was basically positively related to the total number of hydroxyl and carboxyl groups in LMWOAs. The LMWOAs with stronger affinity to lead chromate pigment, lower adiabatic ionization potential (AIP) and higher energy of the highest occupied molecular orbital (EHOMO) are favorable to Cr(VI) reduction by photogenerated electrons and pigment photodissolution. 2.39% of chromium and 10.34% of lead released from the lead chromate pigment in natural conditions during a 6-h sunlight exposure. This study revealed the photodissolution mechanism of lead chromate pigment mediated by LMWOAs with different molecular structures, which helps understand the environmental photochemical behavior of the pigment. The present results emphasize the important role of DOM in the heavy metals release from commercial inorganic pigments.

Effect of extracellular polymeric compositions on in-situ sludge minimization performance of upgraded activated sludge treatment for industrial wastewater

The sludge yield minimization from advanced biological treatment for industrial wastewater could be considered a poorly explored area, therefore, seeks serious attention of the scientific community. Up to best of the knowledge, the extracellular polymeric substances (EPS) profile underlying an upgraded activated sludge treatment (as MANODOX system) for real tannery wastewater has not been addressed in a desired manner. This study covers the elucidation of EPS degradation mechanism and floc morphology underlying MANODOX system for the treatment of real tannery influent. For this purpose, a modified heat extraction method was followed for the estimation of EPS fractions like protein (PN), polysaccharides (PS) and humic contents from the sludge. For the present investigation, the variation in floc characteristics including PN/PS ratio, sludge hydrophobicity, sludge volume index, and facultative microbiota at corresponding change in hydrodynamic sludge retention time (SRT) of 08-40 days was emphasized. The strict maintenance of adapted operational strategies including favoring range of SRT (24 days) for MANODOX implementation succeeded an outstanding in-situ sludge yield minimization lowered up to 0.39 gMLSS/gTCOD that attributed to three times lowered accumulation of PN and PS, comparably lower PN/PS ratio, higher salinity of the mixed liquid, weakened cell-to-cell attachment compared with a parallel run identical aerobic treatment. Here, the reason for improved hydrophobicity and corresponding decline in floc aggregation was attributed to change in sludge PN/PS ratio, carbon to nitrogen ratio of feed influent. The observations confirmed that the sludge yield minimization from MANODOX like systems could be effectively controlled by maintaining aforementioned operational tactics.

Evaluation of the Light/Dark Cycle and Concentration of Tannery Wastewater in the Production of Biomass and Metabolites of Industrial Interest from Microalgae and Cyanobacteria

The tanning industry transforms animal skins into leather and produces liquid effluents with a high organic and inorganic pollutant load. This work evaluated the effect of the tannery wastewater (TWW) concentration and the light/dark cycle on the production of biomass, carbohydrates, proteins, lipids, and pigments (carotenoids and phycobiliproteins) on two microalgae (Chlorella sp. and Scenedesmus sp.) and one cyanobacterium (Hapalosiphon sp.). A non-factorial central experimental design with a response surface was implemented using the STATISTICA 7.0 software. High removal percentages for nitrates (97%), phosphates (73.3%), and chemical oxygen demand (93.2%) were achieved with the three strains. The results also highlight that the use of a constant light regime (24:0) and the concentration of real TWW affect the biomass production, since the highest concentration of biomass recorded was 1.31 g L−1 of Hapalosiphon sp. with 100% undiluted wastewater.

Advanced Oxidation Processes and Biotechnological Alternatives for the Treatment of Tannery Wastewater

The tannery industry is one of the economic sectors that contributes to the development of different countries. Globally, Europe and Asia are the main producers of this industry, although Latin America and Africa have been growing considerably in recent years. With this growth, the negative environmental impacts towards different ecosystem resources as a result of the discharges of recalcitrated pollutants, have led to different investigations to generate alternative solutions. Worldwide, different technologies have been studied to address this problem, biological and physicochemical processes have been widely studied, presenting drawbacks with some recalcitrant compounds. This review provides a context on the different existing technologies for the treatment of tannery wastewater, analyzing the physicochemical composition of this liquid waste, the impact it generates on human health and ecosystems and the advances in the different existing technologies, focusing on advanced oxidation processes and the use of microalgae. The coupling of advanced oxidation processes with biological processes, mainly microalgae, is seen as a viable biotechnological strategy, not only for the removal of pollutants, but also to obtain value-added products with potential use in the biorefining of the biomass.

New Insights into the Microbial Diversity of Cake Layer in Yttria Composite Ceramic Tubular Membrane in an Anaerobic Membrane Bioreactor (AnMBR)

Cake layer formation is an inevitable challenge in membrane bioreactor (MBR) operation. The investigations on the cake layer microbial community are essential to control biofouling. This work studied the bacterial and archaeal communities in the cake layer, the anaerobic sludge, and the membrane cleaning solutions of anaerobic membrane bioreactor (AnMBR) with yttria-based ceramic tubular membrane by polymerase chain reaction (PCR) amplification of 16S rRNA genes. The cake layer resistance was 69% of the total membrane resistance. Proteins and soluble microbial by-products (SMPs) were the dominant foulants in the cake layer. The pioneering archaeal and bacteria in the cake layer were mostly similar to those in the anaerobic bulk sludge. The dominant biofouling bacteria were Proteobacteria, Bacteroidetes, Firmicutes, and Chloroflexi and the dominant archaeal were Methanosaetacea and Methanobacteriacea at family level. This finding may help to develop antifouling membranes for AnMBR treating domestic wastewater.