The determination and origin of fibre clogging in membrane bioreactors

Treatment technologies for bakers' yeast production wastewater

Researchers in recent years have utilized a broad spectrum of treatment technologies in treating bakers' yeast production wastewater. This paper aims to review the treatment technologies for the wastewater, compare the process technologies, discuss recent innovations, and propose future perspectives in the research area. The review observed that nanofiltration was the most effective membrane process for the treatment of the effluent (at >95% pollutant rejection). Other separation processes like adsorption and distillation had technical challenges of desorption, a poor fit for high pollutant load and cost limitations. Chemical treatment processes have varying levels of success but they are expensive and produce toxic sludge. Sludge production would be a hurdle when product recovery and reuse are targeted. It is difficult to make an outright choice of the best process for treating the effluent because each has its merits and demerits and an appropriate choice can be made when all factors are duly considered. The process intensification of the industrial-scale production of the bakers' yeast process will be a very direct approach, where the process optimisation, zero effluent discharge, and enhanced recovery of value-added product from the waste streams are important approaches that need to be taken into account.

Economic evaluation of the reuse of brewery wastewater

Freshwater scarcity is a global concern, not just in countries with limited water resources, and wastewater reuse is becoming an essential necessity. Beer is the fifth-most widely consumed beverage in the world and breweries are a major industrial water consumer. Within this study, the long-term performance of a modular pilot scale plant reusing brewery wastewater was investigated. The system consisted of a flotation device, a membrane bioreactor (MBR), an ultrafiltration (UF) and a reverse osmosis (RO) system. The system was fed with wastewater from the effluent of a full-scale anaerobic reactor. The combination of flotation device and MBR removed chemical oxygen demand (COD) by 93.6%. The subsequent UF and RO removed remaining organic load and inorganic components and process water was produced, whereby drinking water quality was achieved. A yield of 63% was reached with the pilot plant. Based on the results, a base case cost estimate was carried out for a full-scale application, taking into account the actual hydraulic load of the brewery. In order to predict the uncertainties of cost-sensitive factors, the specific costs for sludge disposal, electrical energy, freshwater supply and wastewater disposal as well as membrane lifespan and yield of the RO unit were expressed by probability distributions. Using the Monte Carlo method with 75,000 iterations, the probability distributions for the costs and economic viability of reusing brewery wastewater were calculated. The estimate found that reusing brewery wastewater can be economically viable in 77.2% of simulated cases showing the strongest dependency on costs for wastewater disposal.

Innovative sludge pretreatment technology for impurity separation using micromesh

In order to reduce the impacts on sludge treatment facilities caused by impurities such as fibers, hairs, plastic debris, and coarse sand, an innovative primary sludge pretreatment technology, sludge impurity separator (SIS), was proposed in this study. Non-woven micromesh with pore size of 0.40 mm was used to remove the impurities from primary sludge. Results of lab-scale tests showed that impurity concentration, aeration intensity, and channel gap were the key operation parameters, of which the optimized values were below 25 g/L, 0.8 m³/(m² min), and 2.5 cm, respectively. In the full-scale SIS with treatment capacity of 300 m³/day, over 88% of impurities could be removed from influent and the cleaning cycle of micromesh was more than 16 days. Economic analysis revealed that the average energy consumption was 1.06 kWh/m³ treated sludge and operation cost was 0.6 yuan/m³ treated sludge.

Clogging vs. fouling in immersed membrane bioreactors

Whilst the fouling of MBR membrane surfaces has been very extensively explored by the academic community, there is an increasingly widespread recognition by practitioners of the issue of clogging of membrane channels with sludge solids, sometimes termed "sludging". The study undertaken has quantified this phenomenon using a bespoke test cell allowing a flat sheet membrane channel to be viewed directly during operation and the accumulated solids determined by digital image processing. Sludging behaviour has then been correlated both with the sludge properties, from sludge samples taken from both an industrial and municipal MBR, and the permeability decline rate data. The work has revealed the expected trends in fouling propensity, as quantified by the exponent n of the Δp/Δt = m.exp(nJ) correlation from classical flux-step tests. With zero membrane aeration the industrial samples exhibited sludging, the filling of the complete thickness of the membrane channel with sludge solids, whereas for municipal sludge the solids formed a cake layer which did not fill the channel. In the absence of sludging the permeability decline followed the expected pattern of increasing at the elevated soluble COD and capillary suction time values of the industrial sludge, compared with municipal sludge at the same solids concentration range (8-12 g.L^-1). However, there was no evident correlation between fouling (permeability decline without sludging) and sludging: incipient sludging did not appear to influence permeability, though can be assumed to negatively impact on long-term operation, or relate to the sCOD concentration. Sludging instead appeared to depend on the sludge physical properties, and primarily the viscosity: sludge samples at high viscosities were found to exhibit a different air-scour pattern to that at normal MLSS concentrations. Outcomes suggest that sludging is caused by rheological conditions promoting bubble coalescence and bubble stream constriction, reducing the exposure of the membrane surface to scouring air.

Outside-In Hemofiltration for Prolonged Operation without Clogging

Hemofiltration (HF) is used extensively for continuous renal replacement therapy, but long-term treatment is limited by thrombosis leading to fiber clogging. Maximum filter life is typically less than 20 hours. We have achieved for the first time continuous and consistent hemofiltration for more than 100 hours using outside-in hemofiltration with the blood flow into the inter-fiber space (IFS). Although thrombi do deposit in the IFS, they have minimal affect on the blood flow and filtrate flux due to the three-dimensional system of interconnected hydrodynamic flow channels in the IFS. Microscopic examination of sections of the fiber bundle showed that deposited thrombi have dimensions about the size of the gaps between the hollow fibers and remain isolated from each other. A simple mathematical model is developed to describe the effect of thrombus deposition on the fluid flow that accounts for the enhanced performance arising from the interconnected flow. The hydrodynamic advantage of outside-in HF decreases at low anticoagulant concentration due to the instability in the blood and the very high volume fraction of thrombi that deposit in the entrance zone of the filter. These results clearly demonstrate the significant potential advantages of using outside-in hemofiltration for long-term renal replacement therapy.

A practitioner's perspective on the application and research needs of membrane bioreactors for municipal wastewater treatment

The application of membrane bioreactors (MBRs) for municipal wastewater treatment has increased dramatically over the last decade. From a practitioner's perspective, design practice has evolved over five "generations" in the areas of biological process optimization, separating process design from equipment supply, and reliability/redundancy thereby facilitating "large" MBRs (e.g. 150,000 m(3)/day). MBR advantages and disadvantages, and process design to accommodate biological nutrient removal, high mixed liquor suspended solids concentrations, operation and maintenance, peak flows, and procurement are reviewed from the design practitioner's perspective. Finally, four knowledge areas are identified as important to practitioners meriting further research and development: (i) membrane design and performance such as improving peak flow characteristics and decreasing operating costs; (ii) process design and performance such as managing the fluid properties of the biological solids, disinfection, and microcontaminant removal; (iii) facility design such as equipment standardization and decreasing mechanical complexity; and (iv) sustainability such as anaerobic MBRs.

Immersed membrane bioreactors: an overview with special emphasis on anaerobic bioprocesses

Immersed membrane bioreactor (IMBR) has emerged as a novel potential technology which is considered globally as potent technology, primarily for wastewater treatment. It offers quality improvement in effluents treatment compared to other technological systems. It also offers potential benefits for the bioprocesses where product formation and separation is desired simultaneously in a compact container. This review gives insight for the wide range applications of IMBR focussing on anaerobiosis. It discusses the significance, advantages and drawbacks of IMBR against the conventional methods, highlighting the external membrane bioreactors. While the commercial significance of IMBR is obvious for industrial and municipal wastewater treatment, the current focus is shifting on other applications such as anaerobic bioprocesses. Though the IMBR technology is generally considered hand-in-hand as sustainable technology, the major bottleneck in its application at commercial scale for wastewater treatment seems its economic feasibility and compatibility. Among the technical issues, the membrane fouling is considered as a major problem for which several strategies have been developed to overcome the problem, though there is no complete or universal solution to this problem.

Efficacy of relaxation, backflushing, chemical cleaning and clogging removal for an immersed hollow fibre membrane bioreactor

A pilot-scale hollow fibre immersed MBR, challenged with real municipal wastewater, was studied and operated under conditions identical to those prevailing at full-scale to assess the relative influence of backflushing, relaxation, chemical enhanced backflushing (CEB) and declogging on permeability decline and recovery. The influence of relaxation and backflushing was initially assessed using the conventional flux step method; results indicated reversible fouling to be similar for each method, whilst the irreversible fouling rate was significantly reduced by backflushing. For a given total backflush volume, fouling mitigation was found to be marginally better through employing higher backflush fluxes than longer backflush durations. The impact of the CEB on permeability recovery assessed at low and high fluxes indicated operation at more conservative fluxes to yield more sustained permeability. Under more aggressive operating conditions--fluxes of up to 35 L m⁻² h⁻¹ at specific aeration demand values of 0.25 Nm³/(m² h)--long-term permeability decline took place which was not significantly ameliorated by chemical cleaning. On declogging the membrane through gentle agitation permeability recovery was significant, but was followed by a rapid permeability decline over the course of a few hours. Results suggested control of clogging to be of greater importance than that of fouling in sustaining permeability.