Polyurethane rotating disc system for post-treatment of anaerobically pre-treated sewage.

The performance of polyurethane rotating discs (RBC-1) versus polystyrene rotating discs (RBC-2) for the treatment of an up-flow anaerobic sludge blanket (UASB) reactor effluent fed with domestic wastewater was investigated. Both RBC units were operated at the same organic loading rate (OLR) of 10.5 gCOD/m(2) d. and a hydraulic retention time (HRT) of 2.5 h. The residual values of COD fractions (COD(suspended), COD(colloidal) and COD(soluble)) in the treated effluent of RBC-1 and RBC-2 were similar. However, the removal efficiency of ammonia in the RBC-1 (87 +/- 4%) was significantly higher than that found for RBC-2 i.e. 24 +/- 6%. Moreover, RBC-1 achieved a substantial removal efficiency of 99.0 +/- 1% for Escherichia coli (E. coli), while RBC-2 removed 91.2 +/- 0.3%. Based on these results, optimization of RBC-1 treating UASB reactor effluent was extensively performed. The RBC-1 was operated at an OLR's of 4.0, 11 and 23 gCOD/m(2) d. The results obtained showed that increasing the OLR from 11.0 to 23.0 gCOD/m(2) d and decreasing the HRT from 2.5 to 1.25 h significantly declined the effluent quality of COD(total) and ammonia. However, the residual values of COD(total) and ammonia remained unaffected when increasing the OLR from 4.0 to 11.0 gCOD/m(2) d and by decreasing the HRT from 5 to 2.5 h. Bacteriological examination showed that the mean residual count of E. coli remained at a level of 10(4)/100 ml, in the effluent of RBC-1 independent on the imposed HRT. Accordingly, it is recommended to operate RBC-1 for treatment of anaerobically pre-treated sewage at an OLR of 11 gCOD/m(2) d and an HRT of 2.5 h. A feed-less (ammonia limitation) period of 9.0 days followed by 9.0 days feeding with high OLR of 26 gCOD/m(2) d. (raw sewage) was investigated to elaborate, if the nitrifiers of the RBC-1 are capable to convert ammonia to nitrate after totally 18 days when retuning back to the normal operating conditions. The results of the experiment clearly show a strong and immediate detrimental effect of imposing high OLR of 26 gCOD/m(2) d on the nitrification process in the nitrifying RBC unit. However, after returning back to the original OLR of 10.6 gCOD/m(2) d, the nitrification efficiency in the RBC unit was recovered within 2-3 days.

Sequential anaerobic-aerobic treatment for domestic wastewater - a review.

Introduction, consolidation and even standardization of expensive conventional aerobic systems for domestic wastewater treatment imposed significant financial constraints on the expansion of sanitary services including treatment in developing countries. A viable alternative is the sequential anaerobic-aerobic systems. If compared with the conventional aerobic technologies based on activated sludge processes, lower energy consumption and lower excess sludge production can be achieved with a high-rate anaerobic pre-treatment step. Particularly with concentrated sewage, the energy benefit of applying anaerobic pre-treatment will become very significant. This study aims on putting the effectiveness of sequential systems for treatment of domestic wastewater on view, through displaying results presented in literature on the performance of these systems.

Development of a test method to assess the sludge reduction potential of aquatic organisms in activated sludge.

This article shows the development of a quantitative sludge reduction test method, which uses the sludge consuming aquatic worm Lumbriculus variegatus (Oligochaeta, Lumbriculidae). Essential for the test are sufficient oxygen supply and the presence of a non-stirred layer of sludge for burrowing of the organisms. The test eliminates the unwanted effects of the organisms' movements, so-called bioturbation, on oxygen transport and (therefore) on sludge reduction. We used fresh untreated activated sludge grown on sewage, in order to stay close to the daily practice of sludge treatment. By separating sludge and worms, sludge reduction and worm growth are quantified independently and accurately. Predation by L. variegatus approximately doubles the decay rate of activated sludge. A minimum ratio of initial worm to sludge biomass (W0/S0) of about 0.4g worm/g sludge dry mass is required. Under the test conditions 20-40% of the predated sludge is converted into worm biomass. Our test is simple, reproducible and accurate and is done with equipment generally available in any laboratory, yielding results within a few days. The test can also be used to assess the application of mixtures of different aquatic organisms, but does not provide enough information for the design of a sludge treatment reactor.

Turbidity-based monitoring of particle concentrations and flocculant requirement in wastewater pre-treatment.

The removal of particulate organic material in the first step of wastewater treatment may result in significant savings of reactor volume and energy at wastewater treatment plants, because the organic loading to pursuing unit operations can be reduced. This article describes experiments into the possibility of using turbidity measurements as a tool to quantify the concentration of particles in raw wastewater and, based on the result, assess the organic polymer requirement. A feed forward polymer dosing strategy based on a fixed polymer to influent-turbidity ratio was developed and tested. The experimental work confirms that turbidity measurements can be used to quantify particulate COD. For the investigated wastewater (both untreated and flocculated samples) a linear relationship was found in a wide range of particulate COD (100-900 mg O2 x l(-1)) and turbidity (50-450 NTU). On-line turbidity measurements showed that the particle concentrations in the tested municipal wastewater varied significantly. During dry weather conditions the turbidity fluctuated from 100 to 400 NTU, while in rainy periods fluctuations of 100 to >1,000 NTU were measured. The tested turbidity-related polymer dosing method could be used to create different, constant levels of particle removal, despite large particle concentration variations in the influent. Moreover, it resulted in higher removal efficiencies and a more stable operation compared to the dosing of fixed polymer dose per unit of volume.

Treatment of domestic sewage in a combined UASB/RBC system. Process optimization for irrigation purposes.

A Rotating Biological Contactor (RBC) was fed with raw domestic wastewater or anaerobic effluents. The experiments were conducted at increasing operational temperatures viz. 11, 20 and 30 degrees C to assess the potential increase in removal efficiencies for the different COD fractions (COD(total), COD(suspended), COD(colloidal) and COD(soluble)), E. coli and in the nitrification rate. The results clearly show that, the RBC at HRT of 2.5 h and OLR of 47 g COD/m2 x d provided a very high residual COD(total) value of 228 mg/l when treating domestic wastewater. This was not the case as compared to the results obtained for the system when operated at the same HRT but at lower OLR's of 27, 20 and 14.5 g COD/m2 x d with a UASB effluent at operational temperatures of 11, 20 and 30 degrees C respectively. The residual COD(total) values amounted to 100, 85 and 72 mg/l in the final effluents. Moreover, a high removal of ammonia and low residual values of E. coli was found for the RBC when treating a UASB effluent at operational temperature of 30 degrees C as compared to the situation for treatment of domestic wastewater and UASB effluent at lower temperatures of 11 and 20 degrees C. It can be concluded that an efficient pre-treatment of sewage implies a substantial reduction of OLR applied to the RBC and consequently improves the residual of COD(total) ammonia and E. coli in the final effluent. Therefore, this study supports using a combined system UASB/RBC for treatment of domestic wastewater for reuse in irrigation.

Combined biological and physico-chemical treatment of filtered pig manure wastewater: pilot investigations.

Combined biological and physico-chemical treatment of filtered pig manure wastewater has been investigated on the pilot installation operated under ambient temperatures (15-20 degrees C) and included: i) UASB-reactor for elimination of major part of COD from the filtrate; (ii) stripper of CO2 + fluidised bed crystallisator for phosphate (and partially ammonia) removal from the anaerobic effluents in the form of insoluble minerals-struvite (MgNH4PO4) and hydroxyapatite (Ca5(PO4)3OH); (iii) aerobic-anoxic biofilter for polishing the final effluent (elimination of remaining BOD and nutrients). Under overall hydraulic retention time (HRT) for the system of 7.8 days, the total COD, inorganic nitrogen and total phosphorous removals were 88, 65 and 74%, respectively. A decrease of the overall HRT to 4.25 days led to 91, 37 and 82% removals for total COD, inorganic nitrogen and total phosphorus removals, respectively. The approaches for further improvement of effluent quality are discussed.

Mesophilic and thermophilic activated sludge post-treatment of paper mill process water.

Increasing system closure in paper mills and higher process water temperatures make the applicability of thermophilic treatment systems increasingly important. The use of activated sludge as a suitable thermophilic post-treatment system for anaerobically pre-treated paper process water from a paper mill using recycled wastepaper was studied. Two lab-scale plug flow activated sludge reactors were run in parallel for 6 months; a thermophilic reactor at 55 degrees C and a reference reactor at 30 degrees C. Both reactors were operated simultaneously at 20, 15 and 10 days SRT. The effects of temperature and SRT on sludge settleability and chemical oxygen demand (COD) removal efficiencies of different fractions were studied. Total COD removal percentages over the whole experimental period were 58+/-5% at 30 degrees C and 48 +/- 10% at 55 degrees C. The effect of the SRT on the total COD removal was negligible. Differences in total COD removal between both systems were due to a lesser removal of soluble and colloidal COD at 55 degrees C compared to the reference system. At 30 degrees C, colloidal COD removal percentages were 65+/-25%, 75+/-17% and 86+/-22% at 20, 15 and 10 days SRT, respectively. At 55 degrees C, these percentages were 48+/-34%, 40+/-28% and 70+/-25%, respectively. The effluent concentrations of colloidal COD in both systems were related to the influent concentration of colloidal material. The thermophilic sludge was not able to retain influent colloidal material as well as the mesophilic sludge causing a higher thermophilic effluent turbidity. Sludge settling properties were excellent in both reactor systems. These were neither temperature nor SRT dependent but were rather caused by extensive calcium precipitation in the aeration tanks creating a very dense sludge. For application in the board industry, a thermophilic in line treatment system seems feasible. The higher effluent turbidity is most likely offset by the energy gains of treatment under thermophilic conditions.

Flotation with polyelectrolytes as a first step of a more sustainable wastewater treatment system.

Within the framework of a research programme into more sustainable wastewater treatment systems based on physical-chemical pretreatment the application of dissolved air flotation (DAF) with polyelectrolytes as a primary treatment was investigated. Experiments with municipal wastewater were carried out in 2.5 I flotation batches and in a 100 I DAF pilot reactor. Two cationic polyelectrolytes (PEs) with molecular weights of 4 x 10(6) g/mol and 8 x 10(6) g/mol, were tested. The higher weight PE was more effective in removing turbidity and was used in the pilot experiments for coagulation/flocculation. Within the pilot system experiments the dry solids concentration of the float layer as well as the removal efficiencies of turbidity, CODparticulate, CODdissolved and nutrients, were studied. Typical results were that the obtained dry solids concentration of the floated sludge was 10%, when the float layer was removed after several hours. By using polyelectrolytes it was possible to remove more than 80% of CODparticulate and turbidity at dosages of 7-8 mg/g influent COD (i.e. 5 mg PE/100 NTU). The removal efficiency of CODdissolved was low. There was a proportional relationship between CODparticulate and turbidity. This led to the conclusions that by introducing a dosing control strategy based on continuous turbidity measurements a constant CODparticulate removal efficiency can be obtained.

Feasibility of the BIOFIX-process for treatment of municipal wastewater.

The feasibility of the so-called BIOFIX-process to treat municipal wastewater was investigated in a pilot-plant. The innovative element of this process is that carrier material to which a biofilm is attached is recirculated between a sorption reactor to take up COD from the wastewater and a reactor where this COD is used for (post-) denitrification. In between the sorption and denitrification reactor the wastewater passes two subsequent reactors for removal of the remaining COD and for nitrification, respectively. The results showed that COD uptake by the biofilm in the sorption reactor with a maximum of 34% of the influent load was far below expectations and did not meet the COD requirement for denitrification (50-60% uptake). Also, 9-21% of the influent load of ammonia was taken up by the biofilm. In the denitrification reactor this ammonia was released to the bulk and in this manner discharged with the effluent without having passed the nitrification reactor. Nitrification was inhibited by the presence of high concentrations of suspended solids (50-60 mgl-1) discharged from a COD removal reactor. Together these bottle-necks caused effluent concentrations which were well above the effluent demands and it therefore can be concluded that the BIOFIX-process is not a feasible process to treat domestic wastewater.

Phosphate recycling in the phosphorus industry.

The feasibility of phosphate recycling in the white phosphorus production process is discussed. Several types of materials may be recycled, provided they are dry inorganic materials, low in iron, copper and zinc Sewage sludge ash may be used if no iron is used for phosphate precipitation in the treatment plant; using Ca or Al, or bio-P-removal, increases the recycling potential of the ash, but Cu and Zn are still present in problematic concentrations. Side stream P recovery as Ca- or Al-phosphates is a more attractive option and is discussed in detail. Manure ash also has too high levels of Cu and Zn. Recycling phosphates from industrial sources is possible in many cases, depending on the source.

The multiple benefits of sports for the disabled.

The multiple benefits of sporting activities for disabled people are reviewed. A recent study in the Netherlands underlines once again the paradoxical situation that only a small number of persons with a disability participate in sporting activities. It is important to promote sports to disabled people themselves and to the parents of young children, and desirable that awareness of the multiple benefits of sporting activities be included in the curricula of trainee rehabilitation professionals. After reviewing international developments, current problems in integration and classification in relation to sports are described. There is a relative neglect of recreational as opposed to competitive and elite sports. In developing countries the introduction of sports could serve as a forerunner to, and even temporary substitute for, a complete rehabilitation system.