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Water reuse from wastewater treatment plants can significantly reduce freshwater demand. Additionally municipal sewage and some industrial wastewaters could be used as sources of nutrients and carbon more effectively than they are used today. Biological treatments have attracted the most attention in wastewater purification, whereas, so far, only a little attention has been paid to the physico-chemical technologies. These technologies could, however, have great potential to recover nutrients when purifying wastewater. In this study, the main emphasis was to study the possibilities to utilize existing physico-chemical unit operations for wastewater purification and nutrients as well as carbon recovery. Unit operations were selected so that they could produce exploitable circular economy products from wastewaters and be assembled in a mobile container for carrying out recovery anywhere that is suitable. The results showed that in a mobile container, solids could be successfully separated from the studied wastewaters by flocculation-assisted solid/liquid separation and then processed into hydrochar by hydrothermal carbonization. Phosphate was precipitated using lime milk as calcium phosphate, and ammonium nitrogen was captured from the wastewater using membrane contactor technology resulting in ammonium sulphate for fertilizer use. Additionally, reverse osmosis retained residual impurities well, producing good quality water for reuse. The techno-economic feasibility seems promising.

Modern pulp mills can produce biofuels and value-added bio-products, such as lignin products. However, these bio-products are often present in solutions that are too dilute to be separated in a cost-efficient manner, and concentration by filtration is difficult due to their high fouling properties. In this research, challenging liquor, tannin-containing spruce bark extract, was concentrated by forward osmosis using soda ash from the soda recovery boiler as a draw solution. Soda ash, which consists of about 90% sodium sulphate, could be considered as a cost-free draw solution, since part of it needs to be discharged daily in order to prevent enrichment of potassium and chloride in the chemical circulation of pulp mills. Draw properties of soda ash solution were compared with the properties of pure salts, namely sodium sulphate and sodium chloride. Soda ash generated the same osmotic pressure and similar flux than sodium sulphate, but was a weaker draw solution compared with sodium chloride. When the draw solution concentration was 20% at 40°C, the flux was 16 and 13 LMH with soda ash and sodium sulphate, respectively. Using FO, water recovery over 80% could be reached, which is double compared with water recovery obtained by nanofiltration. However, the salt concentration of the feed solution was increased due to the reverse salt flux of the draw solution, which may hinder the further processing of tannin-containing spruce bark extract.

Internal concentration polarization (ICP) severely limits water flux performance in forward osmosis (FO). We investigated the use of ultrasound to mitigate ICP. Various parameters affecting the performance of the novel ultrasonically-assisted FO were studied, such as ultrasonic frequency and constant versus pulsed operation. With either deionized water or polyphenolic tannin solution as the feed and sodium sulphate as the draw solution, the water flux was nearly doubled for a thin film composite FO membrane upon the application of a 20 kHz ultrasound, with stronger enhancement achieved when the ultrasound was applied to the support layer of the membrane. High frequencies of 573 and 1136 kHz had much weaker effects. Pulsed application of ultrasound can significantly reduce the energy consumption of sonication. For the first time, the current study provides compelling evidence that ultrasonic vibrations applied to porous support structure of an FO membrane is highly effective in mitigating ICP.

This study focused on membrane filtration of neutralized pond water, which may be necessary when good quality water is required for hydrometallurgical processes. Neutralized mine water can still have fairly high metal and sulphate levels, which can hinder discharge and reuse possibilities. Both nanofiltration and reverse osmosis are effective in removing metals and sulphate, but scaling can be a severe problem. Microfiltration as a pre-treatment method, although meant for particle removal, seemed to decrease the amount of scalants, thus delayed scaling on the membrane surface and increasing water recovery for both nanofiltration and reverse osmosis. It is possible that the presence of particles in the feed water promoted crystal growth in the turbulent flow and caused the removal of dissolved constituents. Alternatively, supersaturation could have occurred, allowing microfiltration to remove the scalants as particles. The Liqum sensor indicated that redox values started to increase again just before scaling began due to precipitation in the supersaturated membrane concentrate solution. Thus, the sensor seemed to provide real time, in-situ, early-stage scaling warning.

The emerging thin film composite (TFC) forward osmosis (FO) and pressure retarded osmosis (PRO) membranes generally have better separation properties compared with their cellulose triacetate (CTA) counterparts. Nevertheless, their scaling performance has been rarely reported. In the current study, the phenomenon of membrane integrity loss as a result of scaling is reported for the first time for osmotically driven membrane processes (ODMPs). The results show that the TFC membrane suffered marked flux reduction during the scaling in the active-layer-facing-feed-solution (AL-FS) orientation, accompanied with the severe damage of the membrane active layer. The membrane integrity loss is attributed to the scale formation and growth in the confined space between the membrane and the feed spacer. Compared with the CTA membrane, the TFC was more prone to scaling and membrane damage due to its unfavorable physiochemical properties (presence of Ca2+ binding sites and ridge-and-valley roughness). Although antiscalant addition was shown to be effective for scaling control in AL-FS, it was ineffective in the active-layer-facing-draw-solution orientation. The current study reveals the critical need for scaling control in ODMP processes with respect to the membrane integrity and flux stability. The results also have far-reaching implications for FO and PRO membrane design and process operation. MOE (Min. of Education, S’pore) Accepted version

Water is a necessary component in mining industry. Good water quality enables good enrichments and high yields in hydrometallurgical processes. Waste water from mining industry needs to be purified before discharging to keep surrounding environment clean. However, large water volumes and targeting to high removal of harmful compounds can cause strong economical barrier for the water treatment. Forward osmosis (FO) can in mining industry be an attractive technology, especially if one process stream in a mine is concentrated and another stream acts as a draw solution becoming diluted with good quality FO water. FO can be utilized both in concentrating and diluting purposes and thereby is a good addition to water treatment concepts. One example of the concept building is the improvement of settling pond operation by drawing water out from the pond in order to increase the precipitation of gypsum. Good quality water is at the same time taken into the sea water. Dilution of sea water decreases the total dry solid matter of the feed decreasing the operating pressure and thus the processing costs of desalination

RecAsh project (Regular recycling of wood ash to prevent waste production) is coordinated from Sweden and it belongs to EU-Life Environment program. The aim of the project is to promote ash recycling as a forest fertiliser in Sweden and Finland.This is done mainly by different demonstrations on ash classification, granulation, road haulage, forest spreading and system analysis. Wood as is a nutrient-rich and well-granulable fertiliser for peatland forests, which have a lack of mineral nutrients. Peat ash can also be suitable for forest fertilising by adding potassium into it, e.g. in the form of biotite. Some wood ash should be mixed with peat ash to ensure the granulability. For mineral soils it is necessary to add nitrogen to fertiliser if the growth is to be increased. This can be done e.g. by mixing biosludge with ash. In Finland the ash fertilisation has concentrated so far to the forests owned by forest companies. To limit the transportation distances and to have enough spreading areas in general, ash fertilisation must also be promoted to private forest owners. This requires the chemical quality control of ashes and also e.g. granulation to ensure dust-free operation and to avoid alkaline shock in the soil.

Comparisons are made between polypropylene (PP) fibres and polyacrylonitrile (PAN) fibres in order to relate the thermal properties of fibres with the respective fibre mortar behaviour under thermal exposure. Thermogravimetry (TG), differential scanning calorimetry (DSC) and thermochromatography (ThGC) are utilized. When a cementitious fibre mortar is being heated, several physical phenomena occur in the temperature range between 100°C and 200°C. There is a significant difference in the thermal behaviour between PP and PAN fibres. PP fibres melt at 160–170°C. The non‐melting behaviour of PAN fibre together with its rapid exothermic degradation reactions at around 300°C may add risk to the spalling of fibre mortar under rapid thermal exposure.

Results from an experimental study of electric and/or ultrasonic field assisted filtration are presented. Both electric and ultrasonic fields can reduce fouling of the filtration medium and have significant influence on filtration capacity. The extent of filtration improvement is affected mostly by particle size, surface charge, acoustic frequency, and field strengths. Theoretical examinations of the use of electric field and/or ultrasonic field to enhance filtration efficiency were laid out. Some aspects regarding orthokinetic interaction in acoustic agglomeration were considered. Energy consumptions of the filtrations of different suspensions used in experiments were also determined. For pyrite suspension the best results with ultrasound were obtained when filtration was done as follows: 15‐s negative pressure filtration, 15‐s negative pressure filtration with 22‐kHz ultrasonic burst (0.5 s) and 20‐s drying with negative pressure. In this case the moisture content of cake was 7% while in the reference c...