Search

N 2 O emission was studied in a continuous process via nitrite for real urban wastewater treatment. The relationship between the gaseous forms and the liquid kinetic rates of nitritation and denitritation was investigated. N 2 O mass load and global nitrogen mass balance were quantified. The emission factor of the N 2 O (gN 2 O emitted /kg mixed liquor volatile suspended solids [MLVSS]/d) was calculated. Incrementing the nitritation rate permits the reduction of N 2 O emission by 78%. Instead, an N 2 O decrease of 93% was observed by increasing the denitritation velocity. The determinant role of the anoxic phase in the production of dinitrogen oxide was identified. The contribution of N 2 O emission from the anoxic phase (4.8 gN 2 O-N/kgMLVSS/d) was enhanced under limiting denitritation conditions (kd lower than 0.08 kgNOx-N/kgMLVSS/d). N 2 O production increased by five times with the accumulation of nitrites in the solution up to 200 mg/L. Strict correlation between free ammonia concentration and nitritation rate was found as a possible signal of further ammonia oxidizing bacteria selection.

The activated sludge process is the most widely used wastewater treatment. The main drawback of this technology is the excess sludge production (ESP). The ozonation of sludge of the recirculation line is used to reduce the ESP. In this study, ozonation was applied on a fraction of sludge of the recirculation line in a full-scale plant (50,000 population equivalent) at a lower-specific ozone dose (SOD) compared to previous studies. The results of batch tests to predict the main effect of the technology on the biomass activities are reported. Specifically, tests at 0.7-5 g O₃/kg MLVSS (mixed liquor volatile suspended solids) doses were made to evaluate the changes of the nitrification and denitrification rates, the population of phosphate-accumulating organisms and the gravitational properties. A certain reduction of the impact of ozonation on the kinetic parameters of sludge for values of SOD over 2 g O₃/kg MLVSS was found. The present study highlights also the use of the ratio of ozonated biomass to total biomass as an important operative parameter for ozonation in full-scale plants. Reduction in ESP in the wastewater treatment plant was equal to 10% as dry solids applying a SOD from 1.03 to 1.63 g O₃/kg MLVSS. An analysis of the economic cost of the technique is also reported.

The treatment of industrial liquid wastes is placed in a wide context of technologies and is related to the high variability of the influent physical-chemical characteristics. In this condition, the achievement of satisfactory biological unit efficiency could be complicated. An alternate process (AC) with aerobic and anoxic phases fed in a continuous way was evaluated as an operative solution to optimize the performance of the biological reactor in a platform for the treatment of industrial liquid wastes. The process application has determined a stable quality effluent with an average concentration of 25 mg TN L(-1), according to the law limits. The use of discharged wastewaters as rapid carbon sources to support the anoxic phase of the alternate cycle, realizes a reduction of TN of 95% without impact on the total operative costs. The evaluation of the micro-pollutants behaviour has highlighted a bio-adsorption phenomenon in the first reactor. The implementation of the process defined 31% of energy saving during period 1 and 19% for the periods 2, 3 and 4.

Over the past decade, the concept of anaerobic processes for the treatment of low temperature domestic wastewater has been introduced. This paper uses a developed wastewater flowsheet model and experimental data from several pilot scale studies to establish the impact of integrating anaerobic process into the wastewater flowsheet. The results demonstrate that, by integrating an expanded granular sludge blanket reactor to treat settled wastewater upstream of the activated sludge process, an immediate reduction in imported electricity of 62.5% may be achieved for a treated flow of c. 10,000 m(3) d(-1). This proposed modification to the flowsheet offers potential synergies with novel unit processes including physico-chemical ammonia removal and dissolved methane recovery. Incorporating either of these unit operations can potentially further improve the flowsheet net energy balance to between +0.037 and +0.078 kWh m(-3) of produced water. The impact of these secondary unit operations is significant as it is this contribution to the net energy balance that facilitates the shift from energy negative to energy positive wastewater treatment.

The impact of intermittent air sparging on the operation of an anoxic (dissolved oxygen <0.1 mg l(-1)) immersed membrane bioreactor (iMBR) applied to potable water denitrification is discussed. Air sparge length and specific aeration demand per unit membrane area (SAD(m)) were varied to determine impact on oxygen transfer and membrane fouling. For SAD(m)>0.39 m(3) m(-2) h(-1) with sparge lengths of 10 to 60 seconds, a low dissolved oxygen residual of 0.05 to 0.90 mg O(2) l(-1) was formed which typically inhibited denitrification; oxygen transfer efficiency increased with increasing sparge time. Residual oxygen was rapidly consumed at a rate, r(O(2)), of 0.35 mg O(2) l(-1) min(-1). Once oxygen was depleted, denitrification proceeded. When intermittently sparging at a SAD(m)<0.39 m(3) m(-2) h(-1) for 30 seconds (following 10 minute dead-end filtration cycles in the iMBR), no dissolved oxygen residual was observed and a flux of 21 l m(-2) h(-1) was sustained with fouling rates <0.001 m bar min(-1) recorded. This method provides for effective integration of air sparging into anoxic/anaerobic iMBR environments to simplify process design and delivers a tangible reduction in specific energy demand from 0.19 kWh m(-3) (for constant sparging) to 0.007 kWh m(-3).

The paper deals with the results obtained as nitrogen removal and energy savings in a wastewater treatment plant located in the Province of Trento where the vineyards grow on about 1,500 ha (19% of total vineyards of the Province). In the plant the municipal and pre-treated winery wastewater were co-treated. The optimal effluent quality and the reduction of energy consumption were achieved changing the total oxidation process to an alternate cycles (AC) one and applying a remote control system for three months. The characterization of the influent highlighted a remarkable variability of the mass loads mainly determined by the cyclic winemaking periods. The AC application allowed the system to cope with the intense variations of influent nitrogen loadings and to obtain a stable quality of the effluent with an average TN concentration less than 10 mg NL(-1). The nitrogen loading rate (NLR) up to 0.227 Kg TN m(-3) d(-1) was tolerated by the elevated AC control level device to assure successful denitrification performances (from 70% to 90%) also in conditions of COD/TN lower than 7. Comparing the AC with the pre AC conditions, a total energy saving in the range of 13-23% was estimated. Moreover, the specific energy consumptions were reduced to 59% despite the increment of the influent mass loadings.

The potential of membrane bioreactors to enhance the removal of selected metals from low loaded sewages has been explored. A 1400 litre pilot plant, equipped with an industrial submerged module of hollow fibre membranes, has been used in three different configurations: membrane bioreactor, operating in sequencing batch modality, for the treatment of real mixed municipal/industrial wastewater; membrane-assisted biosorption reactor, for the treatment of real leachate from municipal landfills; continuously fed membrane bioreactor, for the treatment of water charged with cadmium and nickel ions. The results show that: (a) in treating wastewaters with low levels of heavy metals (< one milligram per litre concentration), operating high sludge ages is not an effective strategy to significantly enhance the metals removal; (b) Hg and Cd are effectively removed already in conventional systems with gravitational final clarifiers, while Cu, Cr, Ni can rely on a additional performance in membrane bioreactors; (c) the further membrane effect is remarkable for Cu and Cr, while it is less significant for Ni. Basically, similar membrane effects recur in three different experimental applications that let us estimate the potential of membrane system to retain selected metal complexes. The future development of the research will investigate the relations between the membrane effect and the manipulable filtration parameters (i.e., permeate flux, solids content, filtration cycle).

The paper presents the one year results obtained by a small wastewater treatment plant (WWTP) located in a decentralized area. The plant was organized, reusing current structures, introducing an equalization tank, an anoxic selector and the alternate cycles (AC) as technology in the biological process. The experimentation data processed show the excellent quality of the effluent with high removal efficencies for all the macropollutants. Also, the anoxic selector effect allows, in the critical winter period, the decrease in the filamentous bacteria total number, a net improvement of the settling behaviour with an average solid maximum flux value of 3.8 kgMLSSm(-2) h(-1) and a good mixed liquor settleability. The alternate cycles process flexibility consents to well manage the high fluctuations of the influent loadings. The costs comparison of AC process and extended aeration confirms the sustainability of the upgrading., (Copyright IWA Publishing 2008.)