Alessandro Spagni

Nitrogen removal via nitrite in a sequencing batch reactor treating sanitary landfill leachate

The present paper reports the results of the application of a control system, based on artificial intelligence concepts, for the automation of a bench-scale SBR treating leachate generated in old landfills. Attention was given to the nitritation and denitritation processes in order to enhance the nitrogen removal efficiency. Nitrification and nitrogen removal were usually higher than 98% and 95%, respectively, whereas COD removal was approximately 20-30% due to the low biodegradability of organic matter in the leachate from old landfills; therefore, external COD was added to accomplish the denitrification process. Adjusting the length of the oxic phase, almost complete inhibition of the nitrite oxidizing organisms was observed. The results confirm the effectiveness of the nitrite route for nitrogen removal optimisation in leachate treatment. A significant saving of approximately 35% in external COD addition was achieved.

Monitoring the biochemical hydrogen and methane potential of the two-stage dark-fermentative process.

A two-step process has been recently proposed whereby the products of biological hydrogen production processes are used as substrates for biological methane production. The aim of the present study is to evaluate a simple bench-scale batch procedure for measuring the biochemical hydrogen and methane potential of organic substances as a two-step simulated process. Glucose fermentation showed an hydrogen and methane recovery (measured as the ratio of electron equivalents recovered as hydrogen and methane and electron equivalents of the initial substrate added) from the initial substrate of 13.3% and 75.5%, respectively, that approximates mass balance closure. On the contrary, gas recoveries ranging from 61% to 75% were measured from wastes originating from the food-industry. Moreover, the results demonstrate that the substrate origins significantly influence the ratio of H(2) and CH(4) recovery.

Decolourisation of textile wastewater in a submerged anaerobic membrane bioreactor

Azo dye decolourisation can be easily achieved by biological reduction under anaerobic conditions. The aim of this study was to evaluate the applicability of submerged anaerobic membrane bioreactors (SAMBRs) for the decolourisation of dyeing wastewater containing azo dyes. The reactive orange 16 was used as model of an azo dye. The results demonstrated that very high decolourisation (higher than 99%) can be achieved by SAMBRs. Although decolourisation was not significantly influenced by the azo dye concentrations up to 3.2 g L(-1), methane production was greatly inhibited (up to 80-85%). Since volatile fatty acids accumulated in the treatment system with the azo dye concentration increase, methanogenes seem to be the most sensitive microbial populations of the anaerobic ecological community. The results demonstrated that anaerobic process combined with membrane filtration can deal with highly concentrated wastewaters that result from stream separation of industrial discharges.

Optimisation of sanitary landfill leachate treatment in a sequencing batch reactor

A bench-scale SBR was operated for almost three years in an attempt to optimise the treatment of leachates generated in old landfill. The results of the first two years were used to design a monitoring and control system based on artificial intelligence concepts. Nitrogen removal was optimized via the nitrite shortcut. Nitrification and N removal were usually higher than 98% and 90%, respectively, whereas COD (of the leachate) removal was approximately 30-40%. The monitoring and control system was demonstrated capable of optimizing process operation, in terms of phase length and external COD addition, to the varying loading conditions. Using the control system developed, a significant improvement of the process was obtained: COD and N load were increased (HRT decrease) and a significant decrease (approximately 34%) of the ratio of COD added to N leachate content was observed.

Innovative two-stage anaerobic process for effective codigestion of cheese whey and cattle manure.

The valorisation of agroindustrial waste through anaerobic digestion represents a significant opportunity for refuse treatment and renewable energy production. This study aimed to improve the codigestion of cheese whey (CW) and cattle manure (CM) by an innovative two-stage process, based on concentric acidogenic and methanogenic phases, designed for enhancing performance and reducing footprint. The optimum CW to CM ratio was evaluated under batch conditions. Thereafter, codigestion was implemented under continuous-flow conditions comparing one- and two-stage processes. The results demonstrated that the addition of CM in codigestion with CW greatly improved the anaerobic process. The highest methane yield was obtained co-treating the two substrates at equal ratio by using the innovative two-stage process. The proposed system reached the maximum value of 258 mL(CH4) g(gv(-1), which was more than twice the value obtained by the one-stage process and 10% higher than the value obtained by the two-stage one.

Development and permeability of a dynamic membrane for anaerobic wastewater treatment

Dynamic membranes (DMs) have recently been proposed as an alternative to microfiltration and ultrafiltration in membrane bioreactors (MBRs) in order to contain capital and management costs. This study aims to develop an anaerobic dynamic MBR for wastewater treatment by using a large pore-sized mesh. The study demonstrated that a DM can be developed by using a mesh of 200μm pore-size and applying low cross flow velocity. The bench-scale reactor achieved COD removal efficiency between 65% and 92% and proved to be able to remove approximately 99% of the mixed liquor suspended solids, maintaining a solids retention time well above 200d. A significant quantity of biogas was produced by the external dynamic membrane module and was released with the effluent stream. The flux-step experiment, designed to estimate the critical flux in ultrafiltration MBR, can also be used for monitoring the development and stability of DMs.

Enhanced methane production from rice straw co-digested with anaerobic sludge from pulp and paper mill treatment process

Rice straw is a widely available lignocellulosic waste with potential for energy recovery through anaerobic digestion. Lignin slows the hydrolysis phase, resulting in low methane recovery and long digestion periods. Although pretreatment is effective, it often requires high energy inputs or chemicals that are not feasible for farm-scale systems. This study investigates a unique co-digestion strategy to improve methane yields and reduce digestion times for farm-scale systems. By adding both piggery wastewater and paper mill sludge, specific methane yields in laboratory-scale digesters reached the theoretical value for rice straw (i.e. 330LNCH4/kgVS) over the 92-day period. Accelerated hydrolysis of the straw was directly related to the quantity of sludge added. The most stable digester, with sufficient buffering capacity and nutrients, contained equal parts of straw, wastewater and sludge. This approach is feasible for farm-scale applications since it requires no additional energy inputs or changes to existing infrastructure for dry systems.

Nitrogen removal optimization in a sequencing batch reactor treating sanitary landfill leachate.

Biological nitrogen removal via nitrite may represent a promising process for the optimization of nitrogen removal, in particular in the presence of a low biodegradable COD/TKN ratio. In the present study a lab-scale sequencing batch reactor (SBR) was monitored for approximately 2 years to evaluate the use of dissolved oxygen (DO), pH and oxidation-reduction potential (ORP) as monitoring parameters in order to optimize nitrogen removal via nitrite from leachate generated in old sanitary landfills. The SBR manifested a nitrification efficiency exceeding 99% whereas, due to the low biodegradability of the organic matter presents in the leachates, COD removal reached approximately 40% and the addition of external COD was required to accomplish denitrification process. Moreover, the results demonstrate that DO, pH and ORP are reliable parameters for use in the monitoring of nitritation and denitritation processes in SBRs treating landfill leachates. Through manual modification of the length of the SBR phases to achieve nitrogen removal via nitrite, the nitritation and denitritation processes were rendered unstable leading to the saving of 20% in addition of external COD, almost half the theoretically achievable value. Furthermore, the low dissolved oxygen concentration applied during the oxic phases in an attempt to increase the nitritation process would appear to cause the settling characteristics of the activated sludge to deteriorate.

Intelligent monitoring system for long-term control of Sequencing Batch Reactors

This paper discusses the application of artificial intelligence (AI) concepts to the monitoring of a lab-scale Sequencing Batch Reactor (SBR) treating nitrogen-rich wastewater (sanitary landfill leachate). The paper describes the implementation of a fuzzy inferential system to identify the correct switching sequence of the process and discusses the results obtained with six months of uninterrupted operation, during which the process conditions varied widely. The monitoring system proved capable of adjusting the process operation, in terms of phase length and external COD addition, to the varying environmental and loading conditions, with a percentage of correct phase recognition in excess of 95%. In addition, the monitoring system could be remotely operated through the internet via TCP/IP protocol.

Effect of the organic loading rate on biogas composition in continuous fermentative hydrogen production

Some systems did not select for hydrogen-producing microorganisms and an unexpected growth of hydrogenotrophic methanogens was observed, although the reactors were operated under well-defined operating conditions that could result in biohydrogen production. The aim of this study was to evaluate the effect of the organic loading rate (OLR) on the hydrogen and methane composition of the biogas produced in dark fermentative processes. The study was carried out using an upflow anaerobic sludge blanket (UASB) reactor in order to evaluate the OLR effect in systems with sludge retention. During continuous operation, the UASB reactor showed the slow development of methanogenic activity, related to the applied OLR. The results demonstrate that operating an UASB reactor at pH 5.5 is not enough to prevent the acclimation of methanogens to the acidic pH and therefore long-term biohydrogen production cannot be achieved. Moreover, this study demonstrates that OLR also has an effect on the biogas composition, where the higher the OLR the greater the biogas H2 content.