Neutralization of acid and base solutions by Reverse Electrodialysis with Bipolar Membranes: a sustainable way to recover energy

The large amount of acidic wastewaters produced in various industrial processes can have a large economic and environmental impact. Companies producing waste acid solutions have to send them to specific sites for the neutralization with alkaline solutions. However, efforts have been devoted so far to promote the acid recovery or its reuse. In the perspective of a more circular manufacturing approach, the present work proposes for the first time the use of the novel Bipolar Membrane Reverse Electrodialysis technology as a viable on-site way to convert the chemical energy associated to the pH gradient of waste acid/base solutions into electrical energy. Bipolar Membrane Reverse Electrodialysi…

REVERSE ELECTRODIALYSIS FOR POWER PRODUCTION FROM OILFIELD WASTEWATERS

Produced waters (PWs) are wastewaters generated by crude-oil extraction processes. They can present very different characteristics depending on the field location and production process. Dispersed oil, dissolved organics and solid particles are usually the main components. Moreover, PWs can contain a very high quantity of dissolved salts 1, with a total dissolved solid (TDS) concentration up to 300 g/L. Each barrel of extracted oil requires the simultaneous extraction of 3 barrels of produced water2 on average. PWs are often discharged into the sea, or sent in evaporation ponds thus leading to a dramatic environment impact3. Reinjection in the extraction well is currently the most common an…

A validated multi-scale model of a novel electrodialytic acid-base flow battery

Electrical energy storage is crucial for a deeper penetration of intermittent renewable energies, e.g. solar and wind. The Acid/Base Flow Battery (AB-FB) is a novel, sustainable, environmental-friendly storage technology with high energy density1. The process is based on reversible electrodialytic techniques that convert the electrical energy in the chemical energy associated to pH gradients and vice versa. The bipolar membrane electrodialysis process operates in the charge phase, while the bipolar membrane reverse electrodialysis in the discharge phase. The stack consists of repetitive units, called triplets, made up of an anion-exchange membrane, a bipolar membrane, and a cation-exchange …

Long-run operation of a reverse electrodialysis system fed with wastewater solutions

In the framework of Salinity Gradient Power technologies, Reverse ElectroDialysis (RED) is one of the most promising. In RED, two solutions of different salt concentration are fed into a series of alternate compartments, the one fed by the low salinity solution, the other by the high salinity solution. Compartments are separated by anion and cation exchange membranes alternatively piled to form a stack. Selective ion transport from the concentrate compartment to the dilute one across the membranes allows to generate an ionic current, which is eventually converted into electric current by means of suitable electrode compartments closing the stack. Several options for the feed solutions are p…

Occurrence and transformation of illicit drugs in wastewater treatment plants.

Illicit drugs (IDs) and their metabolites have been recently recognized as a new group of water emerging contaminants (ECs) with potent psychoactive properties and unknown effects to the aquatic environment (Pal et al., 2013). IDs are excreted via urine and feces and arrive at wastewater treatment plants (WWTPs) where can reach ppb levels (Castiglioni et al., 2006). Over the past few years, it has been demonstrated that conventional biological processes in WWTPs are not or scarcely able to remove IDs. Thus, they are discharged into water bodies through the treated effluent (Postigo et al., 2011). Therefore, monitoring the IDs concentration in WWTPs can have a twofold advantage: i. increase …

Process modelling of a novel acid-base flow battery based on bipolar-membranes

The storage of electrical energy is crucial for a deeper penetration of renewable energies with intermittent nature, e.g. solar and wind energy. The Acid/Base Flow Battery (AB-FB) is a novel, sustainable, environmental-friendly storage technology with high energy density of the electrolyte solutions. The process is based on reversible electrodialytic techniques with bipolar membranes, which convert the electrical energy in the chemical energy associated to pH gradients and vice versa. The charge phase is a bipolar membrane electrodialysis process, while the discharge phase is a bipolar membrane reverse electrodialysis process. The stack consists of several repetitive units, called triplets,…

LE EMISSIONI DI GAS CLIMALTERANTI DAI SISTEMI MBR

La salvaguardia dell’ambiente pone ad oggi delle nuove sfide nei confronti dei cambiamenti climatici. Invero, il fenomeno del climate change, i cui principali effetti portano ad un innalzamento delle temperature a seguito del rilascio di emissioni di gas climalteranti (i.e., anidride carbonica, CO2; metano, CH4; protossido di azoto, N2O), richiede degli interventi a breve, medio e lungo termine per limitare i sempre più crescenti danni ambientali. Gli impianti di depurazione contribuiscono anch’essi al fenomeno del climate change attraverso le emissioni di gas climalteranti (Global Water Research Coalition – GWRC, 2011; Law et al., 2012; Zhan et al., 2017).

A moving bed membrane bioreactor pilot plant for carbon and nutrient removal

The paper reports the main results of an experimental gathering campaign carried out on a moving bed membrane bioreactor pilot plant conceived for carbon and nutrients removal according to a University of Cape Town scheme. Organic carbon, nitrogen and phosphorus removal, biokinetic/stoichiometric constants, membrane fouling tendency and sludge dewaterability have been assessed during experiments. The achieved results showed that pilot plant was able to guarantee very high carbon removal, with average efficiency of 98%. In terms of nitrification, the system showed an excellent performance, with efficiencies higher than 98% for most of the experiments. This result might be related to the pres…

Greenhouse gas emissions from membrane bioreactors: analysis of a two-year survey on MBRs

The study aims at evaluating the nitrous oxide (N2O) emission from membrane bioreactors (MBRs) for wastewater treatment. With this regards two-years of experimental activities were performed. More specifically, the study investigates the N2O emissions considering multiple influential factors: i. configurations (i.e., sequential batch- SB-MBR; pre-denitrification - DN-MBR; University Cape Town, UCT-MBR and UCT moving bed biofilm reactor, UCT-MB-MBR); ii. wastewater composition (municipal or industrial); iii. Plant operational conditions (i.e., sludge retention time, SRT, carbon-to-nitrogen ratio, C/N, hydraulic retention time, HRT); iv. and membrane modules. Among the overall analysed config…

A new integrated MBR model for wastewater treatment: sensitivity and uncertainty analysis

In this study a new integrated membrane bioreactor (MBR) model is proposed. The model is able to describe the main biological processes aimed at the carbon and the nutrients (nitrogen, N and phosphorus, P) removal coupled with the soluble microbial products (SMP) formation/degradation. Furthermore, the model describes the key physical processes and the interconnection between SMP and membrane fouling. The model was calibrated by adopting data measured during the monitoring of a University Cape Town (UCT) MBR pilot plant. A sensitivity analysis allowed the reduction of the number of model FACTORs to be calibrated from 122 to 45. A good correlation between measured and simulated data was obta…

Parameter estimation and sensitivity analysis of a nitrogen and phosphorus biological removal model

Towards a reduction of greenhouse gas emission from wastewater treatment plants: a new plant wide experimental and modelling approach

The increasing interest in greenhouse gas (GHG) emissions from wastewater treatment plants (WWTPs) has led to the development of new tools for their design and management. Studies about gas emissions show that the sewer collection and the wastewater treatment plant are anthropogenic GHG potential sources, so they contribute to the climate change and air pollution. A wastewater treatment plant receives wastewater from sewers and, while produces treated water for discharge into surface water, emits the three major greenhouse gases, CO2, CH4, and N2O, during the treatment processes, and additional amounts of CO2 and CH4 from the energy demands (Bani Shahabadi et al., 2009). Indeed, energy cons…

Greenhouse gas from moving bed based integrated fixed film activated sludge membrane bioreactors

The present paper reports the results of a nitrous oxide production investigation in a moving bed based integrated fixed film activated sludge (IFAS) membrane bioreactor (MBR) pilot plant designed in accordance with the UCT layout for biological phosphorous removal. Samples of gas and liquid were collected in order to measure the gaseous, as well as the dissolved concentration of N2O. Furthermore, the gas flow rate from each reactor was measured and the gas flux was estimated. The results confirmed that the anoxic reactor represents the main source of nitrous oxide production. A significant production of N2O was, however, also found in the anaerobic reactor, thus indicating a probable occur…

Lab-scale experiments on a novel acid/base electrodialytic flow battery with bipolar membranes

Electrical energy storage has a key role in the development and diffusion of renewable energy technologies. The Acid/Base Flow Battery is an innovative process to store electrical energy in the form of pH and salinity gradients via electrodialytic reversible techniques based on the use of bipolar membranes. During the charge phase, the unit produces acid and alkaline solutions by applying an electric field, during the discharge phase, converts the pH gradient into electrical energy. In this work, several experimental tests were performed in a 10×10 cm2 laboratory-scale unit fed with HCl, NaOH and NaCl solutions, in order to characterize the battery and assess its performance. The effect of …