1,721,068 research outputs found
Do we really need to remove trace pollutants from wastewater? An innovative assessment approach
No full textInterpreting per capita loads of organic matter and nutrients in municipal wastewater: A study on 168 Italian agglomerations
No full textThe size of an agglomeration is expressed in population equivalent, referring to the maximum average weekly load during the year according to the European Directive 271/91. This quantity, multiplied by the daily biochemical oxygen demand (BOD) produced by one population equivalent (which is 60 g d−1 PE−1, by definition), yields the design biodegradable organic load of the wastewater treatment plant. The same agglomeration size is compared against the capacity of the wastewater treatment plant (WWTP) for plant conformity verification by the European Commission. However, field observations show remarkable fluctuations of the daily mass flows entering a WWTP, often considerably below or above the expected load calculated according to the Directive prescriptions. A wrong estimation of the real influent load adversely affects the plant design and operation, and may lead to a misleading verification of its conformity to the agglomeration. In this work, a statistical data analysis on 168 agglomerations was performed, aiming at verifying the consistency between the expected loads of BOD, chemical oxygen demand (COD), nitrogen and phosphorus and the mass flows measured at the treatment plant inlet. Only 30–40% of the total analysed cases were found having an actual load compatible with the expected one. In these cases, the average per capita daily loads of BOD, COD, nitrogen and phosphorus, calculated over 2–3 years data pools, resulted: 44.6 ± 5.9, 82.4 ± 11, 9.4 ± 1.1, and 1.08 ± 0.13 g d−1, respectively, while the daily BOD per capita production of 60 g represented a value in between the 70th and the 90th percentiles of the actual daily load distributions. For the remaining 60–70% of the total cases, variably-remarkable positive or negative discrepancies between the nominal pollutant loads generated by the agglomeration and those measured at the plant inlet could be detected and possible causes were pointed out
Reuse of wastewater: a feasible option, or not? A decision support system can solve the doubt
No full text<p>A wide debate on wastewater reuse has been turning on within the scientific community (and also at the legislative level) for several years. Beyond the undeniable advantages linked to the recovery of a material resource, the typical question plaguing water managers sounds like: “Is this practice feasible, in terms of both technical and economic sustainability?”. To answer their query, we have developed an innovative tool that rates the three actors of the reclamation process (the wastewater treatment plant WWTP, the hydraulic system, and the final user) by means of a waterfall framework based on the following: (i) the definition of meaningful input factors, (ii) the calculation of robust indices, and (iii) the synthesis process up to a final evaluation (numerical values). The model has been successfully applied to several case studies, where the reuse is either already practiced or under study: As a result, the most suitable scenario for reuse (i.e. #1 WWTP), together with the main opportunities (e.g. a crucial increase in water availability for the final user: #1 WWTP) and threats (e.g. the worst quality of the effluent compared to the current source) has been identified. In summary, this tool represents a useful technical support for decision-makers whenever a judgment on reuse feasibility is required.</p
Energy saving for air supply in a real WWTP: Application of a fuzzy logic controller
No full textAn unconventional cascade control system, for the regulation of air supply in activated sludge wastewater treatment plants (WWTPs), was tested. The dissolved oxygen (DO) set point in the aeration tank was dynamically calculated based on effluent ammonia concentration, following a fuzzy logic based approach. First, simulations were conducted, according to the BSM2 protocol, for a general comparison with more conventional control strategies. It turned out that the effluent quality could be improved by 7-8%, based on the EQI parameter. Moreover, the aeration energy requirement could be reduced up to 13%. Subsequently, the system was installed in a full-scale WWTP. While stably complying with the ammonia effluent standard (10 mg/L), excess air supply was prevented, and a reduction of the specific power consumption (kWh/kgCODremoved) of 40-50% was recorded with respect to the previously installed PID controller (fixed DO set point)
Analysis of the variation of costs for sewage sludge transport, recovery and disposal in Northern Italy: A recent survey (2015-2021)
Full text linkThe cost for the recovery/disposal of residues produced by wastewater treatment plants (WWTPs) represents a relevant aspect in the economics of WWTP management. We elaborated and applied a desk-based methodology to analyze tender processes and to investigate quantitatively and qualitatively the variability of unit costs for sewage sludge (EWC 190805) management in Northern Italy from 2015 to 2021. We conducted a qualitative survey for operators of the sector. Unit costs for sludge management increased over time. The unit cost was mostly affected by the type of sludge recovery/disposal being the cost for recovery in agriculture (direct or by composting) lower than incineration and landfilling. Other variables influencing the cost were the distance and discount offered by the contractor. Regulatory and judiciary events determined a sudden increase of sludge disposal costs in Italy between 2017 and 2019. Recovery in agriculture, when practicable, remains the preferable option. Results can orient and support the optimization of sludge management costs and be of interest for future studies at national or European level
Improving the quality of wastewater treatment plant monitoring by adopting proper sampling strategies and data processing criteria
No full textMonitoring is a crucial operation for plant management. However, proper sampling procedures and data processing criteria are not always adopted. Wastewater treatment plants work under dynamic conditions, which poses a challenge for a correct performance assessment. The aim of this work is to analyse some important aspects of wastewater sampling and data processing, to identify case by case methods which should to be adopted in order to obtain reliable and consistent information on plant performance. The study was conducted through simulations and real data analyses. It turned out that: a) the preferable 24-hour composite sampling procedure is the flow-proportional mode; in addition, the required sampling frequency (i.e. the number of sub-samples to be taken to make the 24-h composite sample) increases as the percentage of population discontinuously discharging the monitored substance decreases; b) a Variability Index was defined to help find the minimum sampling frequency (i.e. the number of 24-h composite samples per year) for the calculation of annual mass flows with an acceptable uncertainty; and c) criteria were proposed for the identification of pseudo-steady state periods needed to calculate reliable mass balances and plant performance indicators
Ammonia Stripping from landfill leachate: Process modelling and comparison between bubbole reactor and packed column
No full textTroubleshooting in a full-scale wastewater treatment plant: what can be learnt from tracer tests
No full textThe experimental assessment of the actual reactor hydrodynamic behavior is aimed at detecting possible deviations from the design configuration, as well as suggesting corrective/improving modifications, efficacy of which can be also assessed in the aftermath. The hydrodynamic scheme can be defined by means of tracer tests (stimulus-response method) used for detecting the residence time distribution curve. This study shows the results of three hydrodynamic tests performed on a wastewater treatment plant half-line, in which a biological process (denitrification and oxidation-nitrification) is carried out. Hydrodynamic faults (in terms of dead space and/or flow bypass) were identified, and consequent actions suggested (i.e., change in submerged mixers orientation in the reactors; sinking of the final section of the sludge recirculation pipe below the free surface to avoid foaming phenomena; introduction of new mixed liquor recirculation lines). These actions, together with a careful selection of wastes to be treated, led to an improvement of the overall process performance
Should rheological properties of activated sludge be measured?
No full textThe core of activated sludge monitoring lies in the biological analyses. Anyway,the knowledge of sludge physical characteristics is crucial for a proper management of WWTPs (Waste Water Treatment Plants). One of these physical features is viscosity that, notwithstanding its valuable role has not yet become a routine analysis. This study examined the evolution of rheological properties of two sludges alongside the "purification route" (from the biological reactor up to the sludge treatments). It could been shown that sludges behaved like non-Newtonian fluids and dry solids content strongly affected viscosity values, which reached relatively high values. Microscopic observation of flocs was carried out. Both the sludges revealed similar features, in particular an over-proliferation of filamentous bacteria. This work showed how rheological measurements can be a tool to obtain information on microbiological composition of activated sludge and how it could be related to settleability properties
Promoting biological phosphorus removal in a full scale pre-denitrification wastewater treatment plant
No full textA survey conducted in Italy revealed that less than 0.5% out of a sample of over 2,000 municipal wastewater treatment plants is equipped with an enhanced biological phosphorus removal process. Conditions promoting biological phosphorus removal have been investigated by monitoring three real plants equipped with, respectively: (A) simultaneous chemical precipitation; (B) enhanced biological removal powered by chemical precipitation; (C) tertiary chemical precipitation with evidence of phosphate accumulating bacteria. An anaerobic compartment revealed essential for the growth of these microorganisms, the readily degradable organic concentration in the influent playing a minor role. Mapping dissolved oxygen and oxidation-reduction potential in different compartments of plant (C) was carried out to understand the reasons why phosphate accumulating bacteria were found even in the absence of anaerobic reactor. Finally, the possibility to exploit the biological phosphorus removal in plant (C), by adjusting the aeration conditions, was explored and an economic analysis showed this to be a preferable approach with respect to the chemical removal of phosphorus
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