Michael Beliavski

An integrated UASB-sludge digester system for raw domestic wastewater treatment in temperate climates

To improve the performance of an upflow anaerobic sludge blanket (UASB) reactor treating raw domestic wastewater under temperate climates conditions, the addition of a sludge digester to the process was investigated. With the decrease in temperature, the COD removal decreased from 78% at 28 °C to 42% at 10 °C for the UASB reactor operating alone at a hydraulic retention time of 6 h. The decrease was attributed to low hydrolytic activity at lower temperatures that reduced suspended matter degradation and resulted in solids accumulation in the top of the sludge blanket. Solids removed from the upper part of the UASB sludge were treated in an anaerobic digester. Based on sludge degradation kinetics at 30 °C, a digester of 0.66 l per liter of UASB reactor was design operating at a 3.20 days retention time. Methane produced by the sludge digester is sufficient to maintain the temperature at 30 °C.

Anaerobic degradation pathway and kinetics of domestic wastewater at low temperatures.

The effect of temperatures below 20 degrees C (20, 15 and 10 degrees C) on the anaerobic degradation pathway and kinetics of domestic wastewater fractionated at different sizes was studied in a fluidized-bed batch reactor. The overall degradation pathway was characterized by a soluble fraction degrading according to zero-order kinetics and a colloidal fraction (between 0.45 and 4.5 microm) that first disintegrates into a particulate fraction smaller than 0.45 microm before finally degrading. The colloidal degradation processes follow a first-order kinetic. In contrast, suspended solids (bigger than 4.5 microm) degrade to soluble and colloidal fractions according to first-order kinetics. The colloidal fraction originating from suspended solids further degrades into soluble fraction. These soluble fractions have the same degradation kinetics as the original soluble fraction. The suspended solids degradation was highly affected by temperature, whereas the soluble fraction slightly affected and the colloidal fraction was not affected at all. On the other hand, the colloidal non-degradable fraction increased significantly with the decrease in temperature while the suspended solids slowly increased. The soluble non-degradable fraction was little affected by temperatures changes.

Treatment of dairy wastewater using a vertical bed with passive aeration.

The aim of this research was to investigate the feasibility of treating liquid dairy wastes by a vertical bed equipped with an innovative passive aeration system. The vertical bed (32 liter) was operated by recirculating consecutive batches of liquid waste in the column. Batches of liquid waste were applied at two different rates: 1) each batch was recirculated for 72 hours, and 2) each batch was recirculated for 24 hours. Settled liquid dairy wastes (5000 mg l-1 COD, 2000 mg l-1 BOD and 2500 mg l-1 TSS) were used in the experiments. When the reactor operated with each batch recirculating for 72 hours, the BOD and COD reduction were 66% and 40%, respectively. The vertical bed operated successfully without the need for an additional rest period. The main removal was observed to take place during the first 20 hours. No biomass or solids accumulation was observed indicating that the remaining 52 hours of recirculation were actually used for bed regeneration, i.e.integrated rest period. When the reactor operated with each batch recirculating for 24 hours, the system clogged after 21 days. An additional 24 day rest period was needed in order to free 94% of the initial void space. In this mode, the BOD and COD reduction were 67% and 47%, respectively. The overall COD removal in a complete operational cycle (feeding period followed by a rest period) was 467 g COD m-3 d-1 (996 g COD m- 2 d-1). This value is 1.4 higher than the COD removal obtained in the 72 hour per batch mode and shows the advantage of conventional vertical bed operation of intensive feeding followed by rest period rather than a rest period integrated into the feeding cycle.

Effect of high electron donor supply on dissimilatory nitrate reduction pathways in a bioreactor for nitrate removal.

The possible shift of a bioreactor for NO3(-) removal from predominantly denitrification (DEN) to dissimilatory nitrate reduction to ammonium (DNRA) by elevated electron donor supply was investigated. By increasing the C/NO3(-) ratio in one of two initially identical reactors, the production of high sulfide concentrations was induced. The response of the dissimilatory NO3(-) reduction processes to the increased availability of organic carbon and sulfide was monitored in a batch incubation system. The expected shift from a DEN- towards a DNRA-dominated bioreactor was not observed, also not under conditions where DNRA would be thermodynamically favorable. Remarkably, the microbial community exposed to a high C/NO3(-) ratio and sulfide concentration did not use the most energy-gaining process.

Biological denitrification of brines from membrane treatment processes using an upflow sludge blanket (USB) reactor.

This paper investigates denitrification of brines originating from membrane treatment of groundwater in an upflow sludge blanket (USB) reactor, a biofilm reactor without carrier. A simulated brine wastewater was prepared from tap water and contained a nitrate concentration of 125 mg/l as N and a total salt concentration of about 1%. In order to select for a suitable energy source for denitrification, two electron donors were compared: one promoting precipitation of calcium compounds (ethanol), while the other (acetic acid), no precipitation was expected. After extended operation to reach steady state, the sludge from the two reactors showed very different mineral contents. The VSS/TSS ratio in the ethanol fed reactor was 0.2, i.e., 80% mineral content, while the VSS/TSS ratio in the acetic acid fed reactor was 0.9, i.e., 10% mineral content. In spite of the low mineral content, the sludge from the acetic acid fed reactor showed remarkably excellent granulation and settling characteristics. Although the denitrification performance of the acetic acid fed reactor was similar to that of the ethanol fed reactor, there was a huge difference in the sludge production due to mineral precipitation, with the corresponding negative aspects including increased costs of sludge treatment and disposal and moreover, instability and difficulties in reactor operation (channeling). These arguments make acetic acid a much more suitable candidate for brine denitrification, despite previous findings observed in groundwater denitrification regarding the essential role of a relatively high sludge mineral fraction for stable and effective USB reactor operation. Based on a comparison between two denitrification reactors with and without salt addition and using acetic acid as the electron donor, it was concluded that the reason for the excellent sludge settling characteristics found in the acetic acid fed reactor is the positive effects of higher salinity on granular sludge formation.

High nitrification rate at low pH in a fluidized bed reactor with either chalk or sintered glass as the biofilm carrier

(Received�19�April�2005�andinrevisedform�5�May�2005) Abstract . A nitrification process using a fluidized bed reactor with chalk (solid calcium carbonate) as the biomass carrier and the only buffer agent was studied. The pH established in the reactor varied between 4.5 to 5.5, with lower pH obtained at higher nitrification rates. In spite of the low pH, high rate nitrification was observed with the nitrification kinetic parameters in the chalk reactor similar to those of biol- logical reactors operating at pH >7. results from microsensor measurements refuted the possibility that favorable pH micro-conditions prevailed on the chalk particles and contributed to high reactor performance. In addition, identification of the major bacterial species in the low pH chalk reactors revealed well-known nitrifying bac- - teria. Based on these results, the performance of a fluidized bed reactor with porous sintered glass particles as the carrier for the biofilm (instead of chalk particles) was tested at similar low pH for comparison purposes. In contrast to the common knowledge of the nitrifiers , high sensitivity to low pH, the results from the non-chalk biofilm reactor showed that welllknown nitrifying bacteria have the ability to nitrify at a high rate at low pH in a biofilm reactor using an inert (sintered glass) carrier.

The contribution of suspended solids to municipal wastewater PHA-based denitrification

The role of wastewater suspended solids in denitrification based on intracellular carbon storage was investigated in a biofilm sequencing batch reactor performing alternately anaerobic carbon storage and denitrification. Municipal wastewater as the feeding was compared with filtered wastewater and with acetate. The results show that the amount of PHA (polyhydroxyalkanoates) stored during a cycle was quite similar, irrespective of the substrate type used as feeding (acetate, real wastewater and real wastewater after filtration). PHA storage was limited even under excess chemical oxygen demand (COD) conditions, with a reducing power capacity enough for denitrification of only 25–26 mg/L N. However, when non-filtered wastewater was used, the denitrification capacity was about 50% higher (38 mg/L N) due to the contribution of entrapped suspended solids as the electron donor. In addition, the involvement of the hydrolyzed wastewater suspended solids resulted in a different PHA composition containing a much higher poly-3-hydroxyvalerate content.

Storage-based denitrification with municipal wastewater: influence of the denitrification stage duration

Microbial polyhydroxyalkenoates (PHAs) degradation is the rate limiting step for denitrification which is based on microbial carbon storage. The influence of denitrification stage duration (3, 2 and 1.5 h) on PHA degradation kinetics and denitrification efficiency during PHA-based denitrification of municipal wastewater and acetate-based synthetic wastewater was investigated. PHA degradation kinetics showed a good fit to first-order reaction, with higher rates at higher PHA concentrations. Decreasing the denitrification stage duration from 3 to 2 h resulted in an increase in biomass PHA content with the corresponding higher specific denitrification rate. Moreover, the daily denitrification rates increased by about 30% in both the acetate fed reactor and the wastewater fed reactor. Further decreasing the denitrification stage duration to 1.5 h resulted in a decrease in sludge PHA content in both reactors. The amount of filtered chemical oxygen demand removed by storage and PHA stored, remained similar regardless of the denitrification stage duration.