Industrial wastewater minimization

Industrial pollution emitted to the environment has created a drastic damage to the environment. Natural purification processes such as dilution and dispersion are not applicable due to the enormous amounts of discharged wastes, as they exceed the assimilative capacity of the local environment. Concern about the environment by the general public has forced governments to establish effluent standards for industrial wastes and emissions. Increasing numbers of industries each year has exerted pressure on the environment compelling regulators to further tighten the standards. This has led to modification and improvement in the existing end-of-pipe treatment facilities resulting in higher investment as well as operation and maintenance cost, whereas in recent years, implementation of proactive methods of waste minimization is gaining much attention within industrial sectors. Various waste minimization techniques such as improved housekeeping, change in process technology, change in product, change in input materials, recycling of chemical and raw materials, and recovery of byproducts are discussed in detail. A number of successful examples discussed in this paper indicate that substantial benefits can be gained by implementing waste minimization programs.

Raw materials and process chemical recovery in industrial wastewater pollution control

This article illustrates the different methods employed to recover raw materials and process chemicals in various industries. Although only a few industries such as car painting, metal cutting, electroplating, textile, abattoir and pesticide formulation have been illustrated in case studies, almost all the industries can recover raw materials and process chemicals from their waste streams. The case studies show that the investments on new processes or systems used to recover raw materials and process chemicals have a short payback period and hence bring huge savings to those industries. Thus, each industry should try to recover raw material and process chemicals from waste streams.

By-product recovery in industrial wastewater pollution control

By-products from most industries become waste when they are not recovered. This article gives examples of by-product recovery from industries such as pulp and paper, dairy, pig farm and food processing.

Although the recovery of by-products will require new processes, the investments on those processes will be paid-back easily from the benefits brought by those by-products. Also, in order to have a sustainable development, by-product recover will play a significant role in all industries in the near future.

Modelling based design of a pilot-scale membrane bioreactor for combined nutrient removal from domestic wastewater

A three stage-treatment of domestic wastewater including anaerobic, anoxic and aerobic phases is employed in this study while a clarifier unit is replaced with a submerged membrane in the aerobic unit. The effects of operational parameters on the performance of a pilot scale submerged membrane bioreactor (SMBR) namely hydraulic retention time (HRT), ratio of return activated sludge (QRS), ratio of internal recycle (QIR), solid retention time (SRT) and dissolved oxygen (DO) are evaluated by simulations, using a hybrid model composed of TUDP model, oxygen transfer model, biofouling model due to extra-cellular polymeric substances (EPS) and turbulent shear model. The results showed that anaerobic HRT of 3 hours, anoxic HRT of 6 hours, QRS of 20% and QIR of 300 % are satisfactory in obtaining a high removal efficiency (>90%) of COD, NH4-N, P04-P as well as a less sludge production. An increase of sludge production causes an increase in EPS, which fouls the membrane surface and increase the cleaning cycle of membrane. Operation of 5MBR system at 2 mg/I of DO and 30 days of SRT can extend the membrane cleaning cycle dramatically. The membrane cleaning cycle however is strongly dependent on the initial and terminal specific fluxes and displays inverse power relationships to those fluxes.

Application of floating medium filters for aquaculture wastewater treatment

Filtration is an effective process in removing particles of various nature and sizes that are present in water and wastewater. It has been used as a final clarifying step in water treatment since the19th century. It is becoming increasingly important in the tertiary treatment step of wastewater to produce effluent of superior quality for the purpose of reuse. Filtration is particularly applied when high flow rates of water with relatively low contents of suspended solids have to be treated. In a conventional water or wastewater treatment system, the filters are usually placed after sedimentation units to remove suspended particles, which escape without settling in the sedimentation units. When chemically pretreated and flocculated water is applied to a filter without a prior-solid liquid separation it is called direct filtration.

Biological treatment of oily wastewater from gas stations by membrane bioreactor

In many Asian countries, rapid industrialization and urbanization has led to an increased number of cars, making wastewater from gas stations an important issue of concern in urban environment. This wastewater is characterized by high concentration of oil-water emulsion, which cannot be effectively removed by a conventional gravity separator. An experimental investigation on the treatability of oily wastewater from gas stations using a membrane bioreactor (MBR) system revealed that MBR system could achieve good removal efficiency with stability against shock loading. Optimum operating conditions were found to be at a hydraulic retention time of 4 h and an oil-loading rate of 1.8 kg oil m^sup -3^.d^sup -1^. It was anticipated that adding powdered activated carbon (PAC) in the MBR could help to adsorb the oils. However, operating the MBR with only microbial flocs has an advantage over adding PAC particles into the MBR, since the former condition could provide a prolonged cycle of filtration with a relatively lesser increase in transmembrane pressure.

A case study on waste minimisation and wastewater treatment in starch and noodle factories

A medium scale Mung Bean starch factory was taken in this study to assess the pollution caused by various streams in starch and noodle factories, and to provide the basic information for wastewater management in them. This study shows that the wastewater from starch processing unit with 46~54 tons of production capacity is the main polluting source, contained high values of COD and SS. Also the specific water consumption to process one ton Mung Bean in 16~25m3 is higher that theoretically required one. Methods have been proposed for minimizing and treating the wastewater produced by the factory to overcome the pollution problems. One of the alternatives is to use water in a controlled way by making optimum flow rates on the tab valves, in which water consumption can be brought down. However, bio-treatability of wastewater can be used for treating the total wastewater due to the suitability in characteristics.

Performance of suspended and attached growth MBR systems in treating high strength synthetic wastewater

The performance of laboratory-scale attached growth (AG) and suspended growth (SG) membrane bioreactors (MBRs) was evaluated in treating synthetic wastewater simulating high strength domestic wastewater. This study investigated the influence of sponge suspended carriers in AG-MBR system, occupying 15% reactor volume, on the removal of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP), and compared it to that of SG-MBR. Results showed that the removal efficiencies of COD, TN and TP in AG-MBR were 98%, 89% and 58%, respectively as compared to 98%, 74% and 38%, respectively in SG-MBR. Improved TN removal in AG-MBR systems was primarily based on simultaneous nitrification and denitrification (SND) process. These results infer that the presence of small bio-particles having higher microbial activity and the growth of complex biomass captured within the suspended sponge carriers resulted in improved TN and TP removal in AG-MBR.

Comparative study on performance of yeast and bacterial membrane bioreactors for high salinity wastewater treatment

Two laboratory-scale membrane bioreactor systems were investigated to treat high saline wastewater containing 1,000 mg/L COD and 32 g/L NaCl, namely: the yeast membrane bioreactor (YMBR) and the bacterial membrane bioreactor (BMBR). COD removal of both processes was above 90% at a hydraulic retention time (HRT) of 5 hours (volumetric loading of 5 kg COD/m³.d), sludge retention time (SRT) of 50 days (the MLSS of above 14 g/L and the F/M of 0.4 d-1). Under these operating conditions, the YMBR could run at a ten-fold lower transmembrane pressure with significantly reduced membrane fouling rate compared to BMBR. This may be because of low production of adhesive extracellular polymers (ECP) and the secondary filtration layer formed from large yeast cells. ECP production of bacterial sludge was increased considerably at high salt concentrations (32 g/L and 45 g/L) and long SRTs. For the bacterial sludge, the increased salinity led to increase in ECP, whereas the ECP content of the yeast sludge was relatively small.