Large scale application of French reed beds: municipal wastewater treatment for a 20,000 inhabitant's town in Moldova

Nature-Based Units as Building Blocks for Resource Recovery Systems in Cities

Cities are producers of high quantities of secondary liquid and solid streams that are still poorly utilized within urban systems. In order to tackle this issue, there has been an ever-growing push for more efficient resource management and waste prevention in urban areas, following the concept of a circular economy. This review paper provides a characterization of urban solid and liquid resource flows (including water, nutrients, metals, potential energy, and organics), which pass through selected nature-based solutions (NBS) and supporting units (SU), expanding on that characterization through the study of existing cases. In particular, this paper presents the currently implemented NBS units for resource recovery, the applicable solid and liquid urban waste streams and the SU dedicated to increasing the quality and minimizing hazards of specific streams at the source level (e.g., concentrated fertilizers, disinfected recovered products). The recovery efficiency of systems, where NBS and SU are combined, operated at a micro- or meso-scale and applied at technology readiness levels higher than 5, is reviewed. The importance of collection and transport infrastructure, treatment and recovery technology, and (urban) agricultural or urban green reuse on the quantity and quality of input and output materials are discussed, also regarding the current main circularity and application challenges.

In-depth assessment of microbial communities in the full-scale vertical flow treatment wetlands fed with raw domestic wastewater

A multiphase study was proposed to examine microbial communities linked to the nitrogen cycle in the first stage of four full-scale French vertical flow treatment systems. To this end, denaturing gradient gel electrophoresis (DGGE) was performed for structural assessment and quantitative PCR (qPCR) to enumerate the abundance of ammonia-oxidizing (AOB). 16S rRNA sequencing was used to assess the taxonomic profile followed by putative assessment of functional genes. The samples were collected under different conditions, such as operational time (presence/absence of sludge layer on the surface of the filters), season (winter and summer), sampling depth (0, 15 and 30 cm) and operation cycle (rest and feed periods). A structural disparity was noted in the upper layers, whereas higher similarity at 30 cm was observed highlighting the effect of organic matter on bacterial diversity. The 7th rest day was highlighted by an apparent decline in the microbial community abundance. Additionally, qPCR indicated that the largest amount of AOB was found at 30 cm depth and during the feeding period. From the taxonomic profile, Mycobacterium, Acinetobacter, Flavobacterium, and Nitrospira were the most abundant genre found in all systems. The functional prediction results showed predicted genes linked to the denitrification process. The results suggested that operating time and season were responsible for the pattern of the microbial community behavior. This study allowed us to further understand the bacterial dynamics and to advance the idea of design modifications made in the first stage of the classical French system to improve nitrogen removal are promising.

French vertical flow treatment wetlands in a subtropical climate: Characterization of the organic deposit layer and comparison with systems in France

This paper presents an advanced characterization of the organic fraction of the top deposit layer collected in a French vertical flow treatment wetland (first stage) in operation in Brazil (two units with different organic deposit layer accumulation times), and compares the results with those obtained from studies in France. The organic and inorganic constituents of the samples collected were analysed by biological, chemical and thermochemical methods. The unit with the organic deposit with longer accumulation time (almost 10 years) was characterized as a mature one (organic matter - OM: 51.3 and 52.7%, thermal index - R_TGA: 0.79 and 0.85, humification index - HI: 0.61 and 1.16, respectively for the depths of 0-5 cm and 5-10 cm). The unit with the deposit organic with less than three years of accumulation also presented characteristics of a mature deposit (OM: 61.2%, R_TGA: 0.79, HI: 1.01 for the depth of 0-5 cm), indicating a rapid mineralization of the deposit under the existing subtropical environment. Despite several differences in term of conception, hydraulic and mass loading rates and accumulation rates, the characteristics of the OM of Brazilian deposits were found to be quite similar to the French ones.

Innovative Multistage Constructed Wetland for Municipal Wastewater Treatment and Reuse for Agriculture in Senegal

This paper reports on the performance of using a multistage constructed wetland (CW) to treat municipal raw wastewater and an analysis of its suitability for agricultural irrigation. The pilot plant consists of two stages of vertical flow CWs plus one stage of a horizontal CW built in 2018 with different local materials at the Gaston Berger University Campus, Saint Louis (Senegal). Each CW stage is composed of several filters with different type of media (silex, granite, or river gravel), filtering media depths, and macrophytes (Phragmites and Typha). The physicochemical and microbiological indicators were monitored over six months at each bed inlet and outlet to evaluate the efficiency and achievements of the Senegalese, European, and WHO regulations/recommendations for disposal or reuse in irrigation. This study demonstrates the viability of this new multistage CW design to treat raw municipal wastewater and produce an effluent of good quality suitable for reuse in agriculture. The removal of organic matter, suspended solids, and nutrients was very high (>95% for SS, BOD5 and N-NH4+, >90% for COD and P-PO43−), as was the reduction of microbiological indicators (fecal coliform reduction >5 log units and helminth egg removal of 100%). First, trends related to the influence of design (the type of gravel, filter depth, and type of macrophyte), operational modes, and the CW treatment efficiency were determined. The use of non-crushed gravel and Typha spp. seemed to provide better removal rates. On the contrary, no differences were found between the use of silex or granite gravel. For the studied Senegalese conditions under dry and hot climates, the preliminary results indicate that no resting periods are necessary for vertical flow CWs (VFCWs), thus resulting in a reduction in construction and operation costs. The main outcome of our study is evidence that multistage CWs can provide robust, cost-effective treatments, as well as allow for safe water reuse, which is imperative in areas with severe water scarcity and endemic microbiological waterborne diseases.

The Role of Constructed Wetlands as Green Infrastructure for Sustainable Urban Water Management

Nowadays, it is better understood that the benefits of green infrastructure include a series of ecosystem services, such as cooling, water storage and management, recreation and landscaping, among others. Green technologies are still developing to provide sustainable solutions to the problems that modern cities and peri-urban areas face at an ever-increasing rate and intensity. Constructed wetlands technology is an established green multi-purpose option for water management and wastewater treatment, with numerous effectively proven applications around the world and multiple environmental and economic advantages. These systems can function as water treatment plants, habitat creation sites, urban wildlife refuges, recreational or educational facilities, landscape engineering and ecological art areas. The aim of this article is to highlight the synergies between this green technology and urban areas in order to reconnect cities with nature, to promote circularity in the urban context and to apply innovative wetland designs as landscape infrastructure and water treatment solutions. This approach could be a step further in the effort to mitigate the current degradation process of the urban landscape. Following the concept of green infrastructure, the article presents and suggests ways to integrate wetland technology in the urban environment, namely: (i) stormwater and urban runoff management (storage and treatment of water during storm events) to provide protection from flood incidents, especially considering climate change, (ii) innovative low-impact infrastructure and design solutions for urban wastewater treatment, and (iii) wetland technology for habitat creation and ecosystem services provision.

The State of the Art of Clogging in Vertical Flow Wetlands

Clogging in vertical flow (VF) wetlands is an important process influencing water purification processes. The main contributing factors are the growth of microorganisms within the filter media, the accumulation of suspended solids on top of the wetland, as well as within the filter media. Both processes lead to a decrease of the available pore space, hence changing the soil’s hydraulic properties. This will alter the water flow and cause malfunctioning of the system. This paper summarizes the state of the art of the prevailing physical, biological and chemical processes influencing clogging in VF wetlands. Different design and operational parameters are discussed to give a better understanding on their influence to prevent malfunctioning. Based on a literature review, a detailed overview on experimental as well as modelling studies carried out is presented. The main conclusions are that on the one hand, important insights on clogging processes in VF wetlands have been gained but, on the other hand, design parameters such as intermittent loading operation and the grain size of the filter media are not well represented in those studies. Clogging models use different conceptual approaches ranging from black box models to process based models.

Zootechnical Farm Wastewaters in Ecuador: A Treatment Proposal and Cost-benefit Analysis

This paper presents and discusses the results of a study carried out in Ecuador, where the zootechnical sector represents one of the country’s most important economic activities. It is, however, the source of many environmental problems, including the release of untreated liquid effluents and odorous emissions, and the production and disposal of solid wastes. The main aim of this study was to propose a treatment train for the zootechnical farm wastewater, combining natural systems (i.e., lagoons and subsurface flow beds) with conventional technologies and a cost-benefit analysis. With reference to a specific case study, the different steps of the treatment train were designed and the corresponding construction, operational and maintenance costs evaluated. To better assess the technical and economic feasibility of such a proposal, a cost-benefit analysis was carried out. The social benefit was evaluated by means of the contingent valuation method and a focus on the methodology and collected results was reported. The main findings discussed, in terms of selected treatments, their costs, and the financial and economic analysis of the project, could be useful for administrators, decision-makers and all technicians involved in planning and management of zootechnical farm wastewaters in developing countries, in particular in Latin America.

A full-scale comparison of two hybrid constructed wetlands treating domestic wastewater in Pakistan

Objective of the current work was to monitor the year-round response of full-scale hybrid constructed-wetlands (CWs) treating domestic wastewater under variable continuous flow. Two systems were evaluated: system-I consisted of an anaerobic baffled reactor (ABR) followed by a saturated vertical subsurface-flow (VSSF) CW and a free-water-surface (FWS) CW as a tertiary treatment; system-II consisted of an ABR followed by a horizontal subsurface-flow (HSSF) CW and FWS. Maximum reduction of 80 and 78%, 81 and 82%, 63 and 69%, 79 and 89% for chemical oxygen demand (COD), biological oxygen demand (BOD), total kjeldahl nitrogen (TKN) and total suspended solids (TSS) was achieved in Systems I and II respectively. There was also effective removal (94% and 93%) of the bacterial population in both systems while more than 94% of pathogenic microorganisms were removed. Data from both systems were further used to compute the first-order rate constants for the k-C* model commonly used in CW design. The treatment performance was confirmed to follow a first-order reaction rate, in which the k₂₀ values of chemical oxygen demand (COD), biological oxygen demand (BOD), total kjeldahl nitrogen (TKN), total phosphorus (TP) and total suspended solids were calculated as 165, 117, 133, 7.5 and 78 m yr^-1 respectively for VSSF and 226, 134, 199, 22 and 73 m yr^-1 respectively for HSSF. A positive correlation with temperature was discovered for all parameters in both systems.