Evaluation of wastewater characterization methods.

Wastewater contains various organic components with different physical and biochemical characteristics. ASM No. 1 distinguishes two categories of biodegradable organic matter in wastewater, rapidly and slowly biodegradable. In general there are two methods for wastewater characterization: based on filtration in combination with a long-term BOD test or based on a respirogram. By comparing both approaches, we showed that in wastewater three categories of organic compounds with different biodegradation rates can be distinguished. These categories are referred to as readily biodegradable, rapidly hydrolysable and slowly hydrolysable organic matter. The total biodegradable COD can be found from a long-term BOD-test combined with a curve-fit and the readily biodegradable and rapidly hydrolysable from a respirogram. The slowly hydrolysable is the difference between total biodegradable COD and the sum of readily biodegradable and rapidly hydrolysable COD. Simulation with characterization based on filtration for a pre-anoxic reactor with a certain N-removal compared with the N-removal of the same plant with wastewater according to the modified characterization shows different results of each wastewater, especially with regard to the effluent nitrate concentration.

Dutch analysis for P-recovery from municipal wastewater.

There is a considerable practical interest in phosphorus recovery from water authorities, elementary P-industry, fertilizer industry and regulators in a number of countries. Due to a handful of full-scale plants worldwide, P-recovery can be seen as technically feasible. However, the economic feasibility of P-recovery from sewage can still be judged as dubious. The most important reason for this is that the prices of the techniques (in euro/tonne P) are much higher compared to the prices of phosphate rock. In this paper an analysis is given to recover phosphate from municipal wastewater for the elementary P-industry Thermphos International B.V. and the fertiliser industry Amsterdam Fertilizers B.V. in The Netherlands. Several scenarios are evaluated and the end products of these scenarios are compared to the quality required by both industries. From a Dutch study it became clear that all end products from the final sludge treatment do not provide a good source of secondary phosphate. As a consequence of this, the most preferred possibility for P-recovery is to extract phosphate before sludge goes to the final sludge treatment. Different scenarios can be selected based on the position of P-recovery in the WWTP configuration, the type of P-recovery product, and the precipitation technique. Local conditions will determine which scenario is the most expedient. Because it is more realistic to judge a practical situation instead of theoretical estimations based on literature, some local situations have to be assessed in sufficient detail to gain more feeling for the expenses and possible savings of P-recovery. One important actor that should be involved in the process management around P-recovery, is the national government. Especially, the Government have the responsibility for sustainable development and should have attention for some stimulation of P-recovery in The Netherlands. Water authorities and the P- and fertilizer industry made already some good steps.

Treatment of anaerobically treated domestic wastewater using rotating biological contactor.

A small-scale pilot plant consisting of a three-stage RBC has been investigated for the removal of E. coli, COD fractions and ammonia from the effluent of an UASB reactor treating domestic wastewater. The results obtained reveal that a three-stage system operated at a HRT of 3.0 h represents an effective posttreatment process. The remaining COD in the final effluent was only 51 (+/- 7) mgl(-1). Ammonia concentration was reduced by 67 (+/- 7.6) %. The overall E. coli reduction was 1.39 log10 at an influent count of 6.5 log10 corresponding to an overall removal efficiency of 95.8 (+/- 4.7) %. However, according to prevailing standards, residual E. coli counts are still high for unrestricted reuse for irrigation purposes. When the system was operated at a HRT of 10 h, overall E. coli removal and ammonia reduction were 99.9 (+/- 0.05)% and 92 (+/- 6.5) % respectively. At a HRT of 10 h, recirculation of the 3rd stage effluent to the 1st stage reduced the residual of E. coli in the final effluent from 2 x 10(3) to 9.8 x 10(2)/100ml. Moreover, the recirculation of nitrified effluent from the 3rd stage to the 1st stage increased ammonia removal in the stage 1 from 23 to 43%. This relatively high ammonia removal likely can be attributed to the supply of nitrifiers from 3rd stage to the 1st one.

Assessment of effluent turbidity in mesophilic and thermophilic activated sludge reactors - origin of effluent colloidal material.

Two lab-scale plug flow activated sludge reactors were run in parallel for 4 months at 30 and 55 degrees C. Research focussed on: (1) COD (chemical oxygen demand) removal, (2) effluent turbidity at both temperatures, (3) the origin of effluent colloidal material and (4) the possible role of protozoa on turbidity levels. Total COD removal percentages over the whole experimental period were 66+/-7% at 30 degrees C and 53+/-11% at 55 degrees C. Differences in total COD removal between both systems were due to less removal of soluble and colloidal COD at 55 degrees C compared to the reference system. Thermophilic effluent turbidity was caused by a combination of influent colloidal particles that were not effectively retained in the sludge flocs, and erosion of the thermophilic activated sludge itself, as shown by denaturing gradient gel electrophoresis (DGGE) profiles. DGGE analysis of PCR-amplified 16S rDNA fragments from mesophilic and thermophilic sludge differed, indicating that different microbial communities were present in the two reactor systems. The effects of protozoal grazing on the effluent turbidity of both reactors was negligible and thus could not account for the large turbidity differences observed.

Mesophilic and thermophilic biological post treatment of anaerobic pretreated paper process water in a closed cycle paper mill.

Thermophilic treatment systems are gaining more and more interest due to increasing system closure and higher process water temperatures. The use of activated sludge as a suitable post treatment system for anaerobically pretreated paper process was studied at 30 and 55 degrees C. Two lab-scale plug flow activated sludge reactors were run in parallel for 6 months at 30 and 55 degrees C. Both reactors were operated simultaneously at a 20, 15 and 10 days SRT. The effects of temperature and SRT on sludge settleability and 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. Two major characteristics of the thermophilic reactor were: 1. a lesser removal of soluble COD compared to the mesophilic reactor and 2. a turbid effluent compared to the mesophilic reactor. Thermophilic effluent turbidity was caused by a combination of influent colloidal particles that were not effectively retained in the sludge flocs and an erosion of thermophilic activated sludge itself, as shown by DGGE profiles. DGGE patterns of mesophilic sludge differed from the thermophilic sludge indicating that different microbial communities were present in both reactor systems.