Integration of Forward Osmosis in Municipal Wastewater Treatment Applications

In recent years, the research community has made constant efforts to develop new technologies for the recovery and valorization of water, nutrient and energy content of municipal wastewater. However, the recovery process is significantly limited due to the low-strength of sewage. Over the last 10 years, the Forward Osmosis (FO) process, has gained interest as a low-cost process with low membrane fouling propensity, which can convert municipal wastewater into a concentrated low-volume effluent, characterized by high organic and nutrient concentration. This chapter presents the main configurations that have been implemented for the concentration of municipal wastewater using FO, including their performance in terms of contaminant removal and water/reverse salt flux (Jw/Js). Furthermore, the draw solutions and respective concentrations that have been used in FO for the treatment of sewage are reported, while at the same time the positive and negative characteristics of each application are evaluated. Finally, in the last section of this chapter, the spontaneous FO followed by anaerobic process is integrated in a municipal wastewater treatment plant (WWTP) and compared with a conventional one. The comparison is done, in terms of the mass balance of the chemical oxygen demand (COD) and in terms of the energy efficiency

A review of nature-based solutions for resource recovery in cities

Our modern cities are resource sinks designed on the current linear economic model which recovers very little of the original input. As the current model is not sustainable, a viable solution is to recover and reuse parts of the input. In this context, resource recovery using nature-based solutions (NBS) is gaining popularity worldwide. In this specific review, we focus on NBS as technologies that bring nature into cities and those that are derived from nature, using (micro)organisms as principal agents, provided they enable resource recovery. The findings presented in this work are based on an extensive literature review, as well as on original results of recent innovation projects across Europe. The case studies were collected by participants of the COST Action Circular City, which includes a portfolio of more than 92 projects. The present review article focuses on urban wastewater, industrial wastewater, municipal solid waste and gaseous effluents, the recoverable products (e.g., nutrients, nanoparticles, energy), as well as the implications of source-separation and circularity by design. The analysis also includes assessment of the maturity of different technologies (technology readiness level) and the barriers that need to be overcome to accelerate the transition to resilient, self-sustainable cities of the future

Biological wastewater treatment with the use of membranes

Scarce water resources in several parts of the world have led to an increased interest in wastewater reuse applications and have promoted the development and application of advanced wastewater treatment technologies. The Membrane Bioreactor (MBR) system is an advanced wastewater treatment system which has been adopted the last years for the biological treatment of wastewater instead of the conventional system of Activated Sludge (AS). MBR systems combine biological treatment and membrane filtration for the secondary treatment of wastewater. The membranes are employed in order to separate the final effluent from sludge. Therefore, this system does not employ a secondary sedimentation tank for effluent clarification and consequently the problems of poor sludge settling due to sludge bulking or due to sludge deflocculation are not encountered. Moreover, MBRs achieve a superior effluent quality that is comparable or even superior to tertiary treatment systems as the membranes are an absolute barrier to suspended solids and to colloidal matter. The adoption of MBRs can lift the barriers for the wider adoption of wastewater reuse, since the final effluent meets the stringiest reuse guidelines for unrestricted irrigation, provided that some disinfection is ensured. This is particularly important for countries facing significant water shortage problems such as Greece. The main operational problem associated with MBR systems is that of membrane fouling, which is defined as the gradual deposition of particles at the membrane surface and interior. As the system operates, the transmembrane pressure (TMP) gradually increases for given membrane flux due to membrane fouling. Once the TMP has reached a certain peak value the membrane module must be removed and must be chemically cleaned in order to restore its permeability. A variety of methods are employed during the system operation to limit fouling; these include backwash, coarse bubble-aeration and chemical cleaning at low doses inside the biological reactor. Coarse bubble aeration significantly increases the system's operational cost. However, even with the adoption of these methods fouling gradually builds up and intensive chemical cleaning is required in which case the module is removed from the biological reactor and is placed in a suitable chemical cleaning solution for several hours. The latter method is the most effective for restoring membrane permeability, but shortens the life-time of the membrane and is thus only periodically employed. As it is evident, membrane fouling increases the operational cost of the system. Inevitably, much research has focused on understanding membrane fouling and its mechanisms, on determining the factors that mostly affect it and on determining cost-effective methods for its limitation. Fouling is a highly complex phenomenon which is influenced by several parameters; these can be grouped in four main categories: (1) the membrane properties, (2) the biomass characteristics, (3) the operating conditions and (4) the influent wastewater. The membrane characteristics and the biomass properties directly impact on membrane fouling, while the operating parameters and the influent wastewater mainly influence fouling indirectly through their impact on biomass properties. The main research question that this thesis addresses is the effect of the solids retention time (SRT) and of the sludge properties on membrane fouling. A series of important issues are investigated. These are: • The impact of the solids retention time on biomass properties and consequently on membrane fouling. • The impact of biomass properties on long-term and on short-term membrane fouling. • The dominant fouling mechanisms in both long-term and short-term membrane fouling. • The determination of the dominant fraction of biomass and of extracellular polymeric substances for the solids retention times under investigation. • The impact of the addition of chemical and physical conditioners to sludge in order to minimize membrane fouling. • The heterotrophic and autotrophic biomass activity. • The MBR long-term biological performance. The long-term membrane fouling was investigated through the operation of a pilot scale MBR system for approximately 2,5 years at SRT = 10, 15, 20 and 33 days, while the short-term membrane fouling was investigated with the 60-minute filtration experiments conducted in a batch ultrafiltration system. […][…] Η παρούσα διδακτορική διατριβή έχει ως βασικό στόχο την εξέταση της επίδρασης των λειτουργικών παραμέτρων και των χαρακτηριστικών της βιομάζας στην έμφραξη των μεμβρανών. Η βασική λειτουργική παράμετρος που διερευνάται είναι ο χρόνος παραμονής των στερεών στο σύστημα (θc), ενώ εξετάζεται η επίδραση μιας σειράς ιδιοτήτων της ιλύος στη μακροχρόνια έμφραξη, όπως είναι τα εξωκυτταρικά πολυμερή, τα κολλοειδή, η συγκέντρωση του ανάμικτου υγρού, η διηθησιμότητα και η καθιζησιμότητα της ιλύος. Επιπλέον, στα πλαίσια της παρούσας διατριβής εξετάζεται η επίδραση των χαρακτηριστικών της βιομάζας στη βραχυχρόνια έμφραξη των μεμβρανών. Η μακροχρόνια έμφραξη εξετάζεται με τη συνεχή λειτουργία πιλοτικού συστήματος MBR για διάστημα 2,5 περίπου ετών σε θc = 10, 15, 20 και 33 ημέρες. Η βραχυχρόνια έμφραξη εξετάζεται σε πρότυπο, εργαστηριακό αντιδραστήρα μεμβρανών υπερδιύλισης διακοπτόμενου έργου με διήθηση ιλύος για 60 λεπτά. Παράλληλα, με την εφαρμογή κατάλληλων μοντέλων διήθησης εξετάζονται οι κυρίαρχοι μηχανισμοί έμφραξης, τόσο για τη μακροχρόνια όσο και για τηβραχυχρόνια λειτουργία και εξετάζεται κατά πόσο οι μηχανισμοί αυτοί είναι ταυτόσημοι. Επίσης, εξετάζονται τα κυρίαρχα κλάσματα του ανάμικτου υγρού και των εξωκυτταρικών πολυμερών για τις υπό διερεύνηση λειτουργικές συνθήκες, καθώς και η επίδραση της προσθήκης συγκεκριμένων ουσιών (φυσικών ορυκτών, κροκιδωτικών και κατιονικού πολυμερούς) στη βιομάζα με στόχο τη μείωση της έμφραξης. Η εξέταση της επίδρασης των προσθέτων στη μείωση της έμφραξης πραγματοποιείται στον εργαστηριακό αντιδραστήρα μεμβρανών υπερδιύλισης. Τέλος, εξετάζεται η δραστηριότητα της ετεροτροφικής και αυτοτροφικής βιομάζας καθώς και οι γενικότερες βιολογικές λειτουργίες του συστήματος MBR. […

Controlled Sewage Sludge Alkaline Fermentation to Produce Volatile Fatty Acids to be Used for Biological Nutrients Removal in WWTPs

In municipal wastewater treatment plants (WWTPs), the disposal of sewage sludge accounts for 20-50% of capital and operating expenses. Therefore, technologies that can simultaneously reduce sludge and generate carbon source for improving biological nutrients removal are in demand. The application of sewage sludge alkaline fermentation can provide the external carbon source that is required to remove nutrients via nitrite for the separate treatment of the supernatant produced from the anaerobic digestion of sewage sludge. Existing studies on sewage sludge fermentation use caustic soda or other chemicals to achieve the desirable pH for alkaline fermentation; this practice increases the cost. In this work, the anaerobic supernatant produced from sewage sludge was used to adjust the pH in the fermentation reactor,while the impact of temperature (30 \ub0C and 55\ub0C), pH (8-11), retention time (1-8 days) and initial total solids (TS = 4.5 and 6.5%) concentration of sludge was examined. The highest volatile fatty acids (VFAs) concentration was achieved at a retention time of 6 days, sludge TS = 6.5%, pH = 10&11 and temperature of 55 C. The addition of pre-aerated anaerobic supernatant achieved similar VFAs as the one of similar pH in which caustic soda adjustment took place

Assessing alternative treatment schemes for the decentralized co-treatment of domestic organic waste and wastewater

Assessing alternative treatment schemes for the decentralized co-treatment of domestic organic waste and wastewate

Influence of the Backwash Cleaning Water Temperature on the Membrane Performance in a Pilot SMBR Unit

In this work, different backwash (BW) schemes were applied on identical hollow fiber (HF) membranes in a membrane bioreactor (MBR) treating municipal wastewater. The effect of BW duration (1 min, 3 min and 8 min) and water temperature (8 °C, 18 °C, 28 °C and 38 °C) on membrane fouling were investigated. Specifically, the transmembrane pressure (TMP) drop and the membrane permeability increase caused by the BW was investigated. Furthermore, the time required for the membrane to return to the state just before each BW experiment, was also examined. It was found that membranes presented better operating performance, as the BW temperature and the backwash duration were increased. Specifically, for 1 min backwash duration at the BW temperatures of 8 °C, 18 °C, 28 °C and 38 °C, TMP decreased by 7.1%, 8.7%, 11.2% and 14.2% respectively. For 8 min BW duration at 8 °C, 18 °C, 28 °C and 38 °C, TMP values decreased by 12%, 17.5%, 23.7% and 30.2% respectively. Increased BW water temperature and duration also improved the membrane permeability. Using higher BW water temperatures, more hours were required to return the membranes to the condition just before cleaning. The selected BW water temperatures did not adversely affect the permeate quality

Implementing indirect real time process control and monitoring in a via-nitrite sequencing batch reactor treating nitrogenous anaerobic supernatant

Implementing indirect real time process control and monitoring in a via-nitrite sequencing batch reactor treating nitrogenous anaerobic supernatan

Planning nature-based solutions for water management and circularity in Ljubljana, Slovenia

Sonaravne rešitve (NBS) in krožno gospodarstvo ponujajo nove priložnosti za upravljanje z vodo in kroženje vode v mestih. V procesu k krožnemu upravljanju z vodo z NBS, eksperti, kot so, kot so urbanisti in okoljski/vodarski inženirji, delujejo kot pospeševalci implementacije, zaradi njihovega tehničnega znanja. Poleg tega lahko s svojega poklicnega stališča premagajo ovire in vplivajo na ključne akterje pro implementaciji sonaravnih rešitev. Namen te študije je (i) raziskati ovire, s katerimi se srečujejo strokovnjaki pri širši implementaciji NBS za krožno upravljanje z vodo v Ljubljani (Slovenija) ter (ii) razumeti institucionalno pripravljenost mesta za načrtovanje NBS za krožno upravljanje voda z NBS. Skozi 14 pol-strukturiranih strokovnih intervjujev, in po analizi vsebinskega diskurza so se pojavile tri krovne teme: urbanistično načrtovanje, urbanistično oblikovanje in izvedba NBS. Ugotovitve razkrivajo institucionalno pripravl jenost Ljubljane za sprejemanje in nadgradnjo obstoječih rešitev z NBS, čeprav ovire še vedno obstajajo: neusklajenost strateških ciljev, institucionalna razdrobljenost, pomanjkanje političnih in pravnih okvirjev (pravila o javnem naročanju, zakoni o urbanističnem oblikovanju) in omejeno sodelovanje državljanov.Nature-based Solutions (NBS) and the circular economy offer new opportunities for water management and water circularity in cities. In the process towards circular water NBS planning and implementation, urban practitioners such as urban planners and environmental/water engineers operate as facilitators and change agents due to their technical expertise. Moreover, from their professional standpoint, they can navigate barriers and influence key actors of institutional readiness of cities to uptake NBS. This study aims (i) to explore the barriers that urban professionals face towards the widespread mainstreaming and implementation of NBS for water management and circularity in Ljubljana, and (ii) to understand the perceived institutional readiness for planning NBS for water management and circularity in the city. Through 14 semi-structured expert interviews, and following a content discourse analysis, three overarching topics emerged: urban planning, urban design, and NBS implementation. The findings reveal the institutional readiness of Ljubljana to adopt and upscale solutions like NBS, although barriers still persist: misalignment of strategic goals, institutional fragmentation, lack of supportive policy and legal frameworks (procurement rules, urban design laws), and limited citizen involvement. New approaches and skilled knowledge brokers are required in order to change the narrative of water being perceived as a problem, and to mainstream NBS for water circularity across the city in the future