Cejna Anna Quist-Jensen

Membrane crystallization for salts recovery from brine—an experimental and theoretical analysis

AbstractIntegration of innovative membrane processes such as membrane distillation (MD) and membrane crystallization (MCr) with conventional pressure-driven operations provide interesting gateways to recover water and minerals from brine at cost competitive with traditional techniques and with improved quality of the salts extracted. Membrane development is one of the most important factors for future progress and commercialization of MD and MCr, thus, in this study, the performance of different poly(vinylidene fluoride) membranes have been tested for water production from (1) NaCl solutions, (2) synthetic sea water, and (3) brine. The utilized membranes have also proved their stability in treatment of saturated solutions for the recovery of high-quality epsomite crystals. In desalination, MD and MCr provide, besides water recovery factors above 90%, the possibility to recover minerals from brine that can partly contribute to the existing mineral extraction industry. This study aims also to give an outloo...

Application of Membrane Crystallization for Minerals' Recovery from Produced Water.

Produced water represents the largest wastewater stream from oil and gas production. Generally, its high salinity level restricts the treatment options. Membrane crystallization (MCr) is an emerging membrane process with the capability to extract simultaneously fresh water and valuable components from various streams. In the current study, the potential of MCr for produced water treatment and salt recovery was demonstrated. The experiments were carried out in lab scale and semi-pilot scale. The effect of thermal and hydrodynamic conditions on process performance and crystal characteristics were explored. Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analyses confirmed that the recovered crystals are sodium chloride with very high purity (>99.9%), also indicated by the cubic structure observed by microscopy and SEM (scanning electron microscopy) analysis. It was demonstrated experimentally that at recovery factor of 37%, 16.4 kg NaCl per cubic meter of produced water can be recovered. Anti-scaling surface morphological features of membranes were also identified. In general, the study provides a new perspective of isolation of valuable constituents from produced water that, otherwise, is considered as a nuisance.

Treated Seawater as a Magnesium Source for Phosphorous Recovery from Wastewater—A Feasibility and Cost Analysis

Conventional resources of phosphorous are at high risk of depletion in the near future due to current practices of its exploitation, thus new and improved exploration methodologies need to be developed to ensure phosphorous security. Today, some treatment plants recover phosphorous from municipal wastewater as struvite (MgNH4PO4·6H2O). Magnesium is often added to the wastewater as MgCl2·6H2O to facilitate the phosphorous recovery. However, the use of magnesium increases the costs of the process and is not aligned with sustainable development, therefore, alternative magnesium sources have to be found. The current study analyzes the feasibility of integrated membrane processes for magnesium recovery from seawater for utilization in the phosphorous recovery process. The integrated membrane systems consist of nanofiltration (NF), membrane distillation (MD), and membrane crystallization (MCr). The lowest associated cost is found for standalone NF treatment. However, the additional treatment with MD and MCr produces fresh water and salts like NaCl or potentially other valuable minerals at the expense of low-grade heat.

Acidification and recovery of phosphorus from digested and non-digested sludge

Acidification was used to dissolve phosphorus from digested and non-digested sludge from five wastewater treatment plants in order to make phosphorus accessible for subsequent recovery. More phosphorus was dissolved from digested sludge (up to 80%), with respect to non-digested sludge (∼25%) and the highest release was observed at pH 2. The acid consumption for digested sludge was higher than for non-digested sludge due to the presence of the bicarbonate buffer system, thus CO2 stripping increased the acid consumption. In all the experiments, the sludge was exposed to acid for 1u202fh. For the five tested sludge types, 60-100u202fmmol o-P was released per added mol H2SO4. It was mainly iron and calcium compounds that accounts for the phosphorus release at low pH. The release of heavy metals was in general low (<30%) for all the wastewater treatment plant, as Zn, Cd and Ni showed the most critical release after acidification of non-digested sludge.

Molecular Weight Cutoff

High-temperature electrolysis (also called steam electrolysis) is the water electrolysis at temperatures that ranged between 700 and 1,000 °C in which electrical energy is the driving force of water splitting to produce oxygen (O2) and hydrogen (H2). The core of an electrolysis unit is an electrochemical cell, which is filled with pure water and has two electrodes connected with an external power supply. At a certain voltage, which is called critical voltage, between both electrodes, the electrodes start to produce hydrogen gas at the negatively biased electrode (Eq. 1) and oxygen gas at the positively biased electrode (Eq. 2). The amount of gases produced per unit time is directly related to the current that passes through the electrochemical cell (Wendt and Kreysa 1999)