Towards a modelling framework for nature-based solutions in wastewater treatment.

This article presents the authors' perspectives on modelling best practices for nature-based solutions (NBS). The authors led a workshop on NBS modelling as part of the 8th IWA Water Resource Recovery Modelling Seminar (WRRmod2022+) in January 2023, where the discussion centred around the design, use cases, and potential applications of NBS models. Four real-world case studies, encompassing an aerated lagoon, a biofilm-enhanced aerated lagoon, a stormwater basin, and a constructed wetland were reviewed to demonstrate practical applications and challenges in modelling NBS systems.

Thermal properties of treatment wetlands operated under freezing conditions.

The use of treatment wetlands (TWs) presents particular challenges in regions with sub-zero winter temperatures, due to reduced biological activity and risk of pipe breakage or clogging due to freezing. We studied the vertical temperature distribution in four pilot-scale TWs exposed to winter temperatures in order to determine the impact of operational system parameters and the role of insulation on heat conservation inside the filtering bed. The overall temperature pattern was similar in all wetlands, with a trend of increasing temperature from the surface toward the bottom during the cold season.

Physico-chemical characteristics and biodegradability of primary effluent and particulate matter removed by microscreens.

In this study, the physical, chemical, and biological characteristics of raw wastewater were compared with the liquid and solid streams generated by a primary clarifier (PC), a rotating belt filter (RBF, 350 μm), and a drum filter (DF, 60 μm) and series (SER) combination of an RBF with a PC or a DF using pilot-scale primary treatment units. The RBF removed about 36% of the influent total suspended solids. The DF and PC yielded an influent total suspended solid removal of 47% to 55% in both individual (parallel) and SER configurations.

Treatment of Landfill Leachate by Short-Rotation Willow Coppice Plantations in a Large-Scale Experiment in Eastern Canada.

The treatment of leachate by vegetative filters composed of short-rotation willow coppice (SRWC) has been shown to be a cost-effective alternative to conventional and costly methods. However, few studies have considered the treatment capability of willow filters at a scale large enough to meet the industrial requirements of private landfill owners in North America. We report here on a field trial (0.

Design of a zero liquid discharge leachate treatment system using an evapotranspiration willow bed.

While zero liquid discharge (ZLD) wetlands have been successfully used for domestic wastewater treatment, adapting this technology to treat other wastewaters such as leachate could be very attractive for some industries concerned with meeting increasingly stringent environmental regulations. Leachate treatment typically implies large volume of water that are entirely dependent on rainfall and therefore highly variable both throughout the year and between years. Current design guidelines for zero discharge willow systems limit system flexibility because they are based on rough theoretical estimates of evapotranspiration.

Macrophyte Potential to Treat Leachate Contaminated with Wood Preservatives: Plant Tolerance and Bioaccumulation Capacity.

Pentachlorophenol and chromated copper arsenate (CCA) have been used worldwide as wood preservatives, but these compounds can toxify ecosystems when they leach into the soil and water. This study aimed to evaluate the capacity of four treatment wetland macrophytes, , , and two subspecies of , to tolerate and treat leachates containing wood preservatives. The experiment was conducted using 96 plant pots in 12 tanks filled with three leachate concentrations compared to uncontaminated water.

Establishment and potential use of woody species in treatment wetlands.

Plant species selection is an important criterion for improving treatment wetland performance. The aim of this work was to evaluate removal efficiency and potential uses of woody species in treatment wetlands during the establishment year. Plant development, removal efficiency and evapotranspiration rate of five woody species () and four herbaceous taxa typically used in treatment wetlands () were compared in a mesocosm-scale study during one growing season.

Impacts of Continuous Inflow of Low Concentrations of Silver Nanoparticles on Biological Performance and Microbial Communities of Aerobic Heterotrophic Wastewater Biofilm.

Attached-growth wastewater processes are currently used in water resource recovery facilities (WRRFs) for required upgrades due to an increase in influent loading or to reach more stringent discharge criteria. Yet, the distribution and long-term inhibitory effects of silver nanoparticles (AgNPs) in attached-growth biological wastewater processes and their impact on involved microbial communities are poorly understood at relevant, low concentrations. Retention, distribution, and long-term inhibitory effect of polyvinylpyrrolidone (PVP)-coated AgNPs were evaluated in bench-scale moving bed biofilm reactors (MBBRs), achieving soluble organic matter removal, over a 64 day exposure to nominal concentrations of 10 and 100 μg/L.

Willows for environmental projects: A literature review of results on evapotranspiration rate and its driving factors across the genus Salix.

Willows are increasingly used for a wide range of environmental projects, including biomass production, leachate treatment, riparian buffers and treatment wetlands. Evapotranspiration (ET), assumed to be high for most willow species used in environmental projects, affects hydrological cycles and is of key interest for project managers working with willows. Here, we present a comprehensive review of ET rates provided in the literature for the genus Salix.

Fate and inhibitory effect of silver nanoparticles in high rate moving bed biofilm reactors.

Municipal water resource recovery facilities are the primary recipients of a significant fraction of discharged silver nanoparticle (AgNP)-containing wastes, yet the fate and potential risks of AgNPs in attached-growth biological wastewater treatment processes are poorly understood. The fate and inhibitory effects of polyvinylpyrrolidone (PVP)-coated AgNPs at environmentally-relevant nominal concentrations (10, 100, 600 μg/L) were investigated, for the first time, in high rate moving bed biofilm reactors (MBBRs) for soluble organic matter removal. The behavior and removal of continuously added AgNPs were characterized using single-particle inductively coupled plasma mass spectrometry (spICP-MS).

Steel slag filter design criteria for phosphorus removal from wastewater in decentralized applications.

The objective of this project was to develop a novel phosphorus removal system using steel slag filters applicable in decentralized applications and to propose design criteria about maintenance needs. Slag exhaustion functions were measured on 2-3 mm, 3-5 mm, 5-10 mm and 16-23 mm slag. Three steel slag columns with particle size of 2-3 mm, 3-5 mm and 5-10 mm were fed with the effluent of an aerated lagoon during 589 days.

Development and modelling of a steel slag filter effluent neutralization process with CO-enriched air from an upstream bioprocess.

The main objective of this project was to develop a steel slag filter effluent neutralization process by acidification with CO-enriched air coming from a bioprocess. Sub-objectives were to evaluate the neutralization capacity of different configurations of neutralization units in lab-scale conditions and to propose a design model of steel slag effluent neutralization. Two lab-scale column neutralization units fed with two different types of influent were operated at hydraulic retention time of 10 h.

Numerical simulations with the P-Hydroslag model to predict phosphorus removal by steel slag filters.

The first version of the P-Hydroslag model for numerical simulations of steel slag filters is presented. This model main original feature is the implementation of slag exhaustion behavior, crystal growth and crystal size effect on crystal solubility, and crystal accumulation effect on slag dissolution. The model includes four mineral phases: calcite, monetite, homogeneous hydroxyapatite (constant size and solubility) and heterogeneous hydroxyapatite (increasing size and decreasing solubility).

Effect of ozonation on anaerobic digestion sludge activity and viability.

The effect of ozonation of anaerobic digested sludge on methane production was studied as a means of increasing the capacity of municipal anaerobic digesters. Ozone doses ranging from 0 to 192 mg O/g sludge COD were evaluated in batch tests with a bench scale ozonation unit. Ozonation initially, and temporarily, reduced biomass viability and acetoclastic methanogenic activity, resulting in an initial lag phase ranging from 0.

Activated Sludge Production Parameters and Nutrient Content of Organic Sludge Components.

  An important part of biological treatment system design is quantifying the sludge production and the nutrient removal capacity. Influent wastewater COD fractionation, biomass growth and endogenous respiration directly impacts the composition of the mixed liquor solids in activated sludge systems. The objectives of this project were to determine the model kinetic and stoichiometric parameters associated with activated sludge production and the nutrient content (N and P) of unbiodegradable organic matter components.

Sludge reduction via biodegradation of the endogenous residue (X): experimental verification and modeling.

The feasibility of sludge reduction via the X biodegradation process was explored both experimentally and through modeling, where the main focus was on determining the value of the b parameter (first order degradation of X) from a continuous process. Two activated sludge (AS) systems (30 L) were operated in parallel with synthetic wastewater during 16 months: a conventional activated sludge (CAS) system and a modified low-sludge production activated sludge (LSP-AS) process equipped with a side-stream digester unit (DU). First, the long term data of the CAS reactor (1 year) were used to calibrate the ASM model and to estimate the heterotrophic decay constant of the cultivated sludge (b = 0.

Compact secondary treatment train combining a lab-scale moving bed biofilm reactor and enhanced flotation processes.

High-rate wastewater processes are receiving a renewed interest to obtain energy positive/efficient water resource recovery facilities. An innovative treatment train combining a high-rate moving bed biofilm reactor (HR-MBBR) with an enhanced flotation process was studied. The two objectives of this work were 1) to maximize the conversion of soluble organics to particulate matter in an HR-MBBR and 2) to maximize the particulate matter recovery from the HR-MBBR effluent by green chemicals to enhance biogas production by anaerobic digestion.

Mechanisms for Reduced Excess Sludge Production in the Cannibal Process.

Reducing excess sludge production is increasingly attractive as a result of rising costs and constraints with respect to sludge treatment and disposal. A technology in which the mechanisms remain not well understood is the Cannibal process, for which very low sludge yields have been reported. The objective of this work was to use modeling as a means to characterize excess sludge production at a full-scale Cannibal facility by providing a long sludge retention time and removing trash and grit by physical processes.

Phosphorus removal by steel slag filters: modeling dissolution and precipitation kinetics to predict longevity.

This article presents an original numerical model suitable for longevity prediction of alkaline steel slag filters used for phosphorus removal. The model includes kinetic rates for slag dissolution, hydroxyapatite and monetite precipitation and for the transformation of monetite into hydroxyapatite. The model includes equations for slag exhaustion.

Modelling the degradation of endogenous residue and 'unbiodegradable' influent organic suspended solids to predict sludge production.

Activated sludge models have assumed that a portion of organic solids in municipal wastewater influent is unbiodegradable. Also, it is assumed that solids from biomass decay cannot be degraded further. The paper evaluates these assumptions based on data from systems operating at higher than typical sludge retention times (SRTs), including membrane bioreactor systems with total solids retention (no intentional sludge wastage).

Removal of phosphorus, fluoride and metals from a gypsum mining leachate using steel slag filters.

The objective of this work was to evaluate the capacity of steel slag filters to treat a gypsum mining leachate containing 11-107 mg P/L ortho-phosphates, 9-37 mg/L fluoride, 0.24-0.83 mg/L manganese, 0.

Effects of long exposure to low temperatures on nitrifying biofilm and biomass in wastewater treatment.

Attached growth biological treatment systems are a promising solution to ammonia removal in cold-temperature climates. Environmental scanning electron microscopy (ESEM) and confocal laser scanning microscopy in combination with fluorescent in situ hybridization (FISH) was used to investigate the effects of 4 months of exposure to 4 degrees C on nitrifying biofilm and biomass. These molecular and microscopic methods were modified to minimize loss of mass and distortion of in situ perspectives.

Biodegradation of the endogenous residue of activated sludge in a membrane bioreactor with continuous or on-off aeration.

The goal of this study was to determine the effect of a long sludge retention time on the biodegradation of the endogenous residue in membrane digestion units receiving a daily feed of sludge and operated under either aerobic or intermittently aerated (22 h off-2 h on) conditions. The mixed liquor for these experiments was generated in a 10.4 day sludge retention time membrane bioreactor fed with a synthetic and completely biodegradable influent with acetate as the sole carbon source.

Model of phosphorus precipitation and crystal formation in electric arc furnace steel slag filters.

The objective of this study was to develop a phosphorus retention mechanisms model based on precipitation and crystallization in electric arc furnace slag filters. Three slag columns were fed during 30 to 630 days with a reconstituted mining effluent at different void hydraulic retention times. Precipitates formed in columns were characterized by X-ray diffraction and transmission electronic microscopy.