Psychrophilic treatment of municipal wastewater with a combined UASB/ASD system, and perspectives for improving urban WWTP sustainability.

According to new paradigms of urban wastewater management, energy savings and resources and energy recovery from sewage will assume an ever-increasing importance. Anaerobic processes, aside from being more energy efficient than conventional aerobic ones, are particularly suited to recover embedded organic energy, improving the overall energy balance of treatment processes, however, their performance is limited by low temperatures and slower kinetics. In this study, a pilot Upflow Anaerobic Sludge Blanket (UASB) reactor was operated to treat municipal wastewater at low temperature regime (16.5-18.5 °C) for 22 weeks, both as standalone process and combined with a sidestream anaerobic sludge digester. Process performance highlighted good system robustness, as proved by stable pH and volatile fatty acid/total alkaline buffer capacity ratio, even though observed methane yield was low. Observed COD and TSS removal efficiencies were in the ranges of 60-69% and 63-73%, respectively. Methane production ranged between 0.106 and 0.132 Nm3CH4/kgCODrem. An economic assessment was carried out to evaluate the feasibility and benefits of implementing UASB pre-treatment of municipal wastewater in existing conventional facilities (activated sludge and anaerobic sludge digestion), showing that significant energy demand reduction could be achieved for both biological secondary treatment and sludge management, leading to considerable operational economies, and possible positive economic returns within a short pay-back period (3-4 yrs).

Wastewater fertigation in agriculture: Issues and opportunities for improved water management and circular economy.

Water shortages are an issue of growing worldwide concern. Irrigated agriculture accounts for about 70% of total freshwater withdrawals globally, therefore alternatives to use of conventional sources need to be investigated. This paper critically reviews the application of treated wastewater for agricultural fertigation (i.e., water and nutrient recovery) considering different perspectives: legislation, agronomic characteristics, social acceptability, sustainability of treatment technologies. Critical issues that still need further investigation for a wider application of fertigation practices include accumulation of emerging contaminants in soils, microbiological and public health implications, and stakeholders' acceptance. A techno-economic methodological approach for assessing the sustainability of treated wastewater reuse in agriculture is subsequently proposed herein, which considers different possible local conditions (cultivated crops and effluent characteristics). The results showed that tailoring effluent characteristics to the desired nutrient composition could enhance the process economic sustainability; however, water savings have a major economic impact than fertilizers' savings, partly due to limited P reuse efficiency. The developed methodology is based on a practical approach and may be generalized to most agricultural conditions, to evaluate and encourage safe and efficient agricultural wastewater reuse practices.

Bioelectrochemical treatment of municipal solid waste landfill mature leachate and dairy wastewater as co-substrates.

Despite solid wastes' landfill disposal limitation due to recent European legislation, landfill leachate disposal remains a significant problem and will be for many years in the future, since its production may persist for years after a site's closure. Among process technologies proposed for its treatment, microbial fuel cells (MFCs) can be effective, achieving both contaminant removal and simultaneous energy recovery. Start-up and operation of two dual-chamber MFCs with different electrodes' structure, fed with mature municipal solid waste landfill leachate, are reported in this study. Influent (a mix of dairy wastewater and mature landfill leachate at varying proportions) was fed to the anodic chambers of the units, under different conditions. The maximum COD removal efficiency achieved was 84.9% at low leachate/dairy mix, and 66.3% with 7.6% coulombic efficiency (CE) at a leachate/dairy ratio of 20%. Operational issues and effects of cells' architecture and electrode materials on systems' performance are analyzed and discussed.

Combined microalgal photobioreactor/microbial fuel cell system: Performance analysis under different process conditions.

Increasing energy demands and greenhouse gases emission from wastewater treatment processes prompted the investigation of alternatives capable to achieve effective treatment, energy and materials recovery, and reduce environmental footprint. Combination of microbial fuel cell (MFC) technology with microalgal-based process in MFC-PBR (photobioreactor) systems could reduce greenhouse gases emissions from wastewater treatment facilities, capturing CO2 emitted from industrial facilities or directly from the atmosphere. Microalgae production could enhance recovery of wastewater-embedded resources. Two system MFC-PBR configurations were tested and compared with a control MFC, under different operating conditions, using both synthetic and agro-industrial wastewater as anolytes. COD removal efficiency (ηCOD) and energy production were monitored during every condition tested, reaching ηCOD values up to 99%. Energy recovery efficiency and energy losses were also evaluated. The system equipped with microalgal biocathode proved to be capable to efficiently treat real wastewater, surpassing the effectiveness of the control unit under specific conditions. Oxygen provided by the algae improves the overall energy balance of this system, which could be further enhanced by many possible resources recovery opportunities presented by post-processing of the cathodic effluent.

In situ groundwater remediation with bioelectrochemical systems: A critical review and future perspectives.

Groundwater contamination is an ever-growing environmental issue that has attracted much and undiminished attention for the past half century. Groundwater contamination may originate from both anthropogenic (e.g., hydrocarbons) and natural compounds (e.g., nitrate and arsenic); to tackle the removal of these contaminants, different technologies have been developed and implemented. Recently, bioelectrochemical systems (BES) have emerged as a potential treatment for groundwater contamination, with reported in situ applications that showed promising results. Nitrate and hydrocarbons (toluene, phenanthrene, benzene, BTEX and light PAHs) have been successfully removed, due to the interaction of microbial metabolism with poised electrodes, in addition to physical migration due to the electric field generated in a BES. The selection of proper BESs relies on several factors and problems, such as the complexity of groundwater and subsoil environment, scale-up issues, and energy requirements that need to be accounted for. Modeling efforts could help predict case scenarios and select a proper design and approach, while BES-based biosensing could help monitoring remediation processes. In this review, we critically analyze in situ BES applications for groundwater remediation, focusing in particular on different proposed setups, and we identify and discuss the existing research gaps in the field.

Simulation tests of in situ groundwater denitrification with aquifer-buried biocathodes.

Bioelectrochemical systems (BES) application was proposed for a variety of specific uses, due to these systems' characteristics: electrodes can act as virtually inexhaustible electron acceptors/donors, offering a growth-support surface for microorganisms, and stimulating naturally-occurring microbial degradation activities. In situ, groundwater denitrification therefore seems to be a potential candidate for their use. In this study, buried biocathodes were operated in laboratory settings for the simulation of in situ groundwater denitrification. Two alternative configurations were tested: biocathode buried in sand, and biocathode buried in gravel. A control test with a biocathode in absence of sand/gravel was also performed. In all the cases, biocathodes were driven by power supply or potentiostat to guarantee a steady electron flux to the cathode. The presence of sand and gravel strongly influenced the denitrification process: in both configurations, accumulation of intermediate N-forms was detected, suggesting that the denitrification process was only partially achieved. In addition, a significant decrease (in the 20-36% range) in nitrate removal rates was measured in sand and gravel setups compared to the control reactor; this issue could be attributed to lack of recirculation that limited contact between substrate and electrode-adherent biofilm. Biocathodes buried in gravel obtained better results than those buried in sand due to the lower packing of the medium. The results of this study suggest that, in order to achieve successful in situ treatment, special design of submerged-biocathodic BESs is necessary.

Controlled sequential biocathodic denitrification for contaminated groundwater bioremediation.

Nitrate groundwater contamination is a worldwide concern. In this study, a novel 2-stage, sequential biocathodic denitrification system was tested to perform autotrophic denitrification of synthetic groundwater. The system was operated at different nitrate loading rates (66-301 gNO3--N m-3NCC d-1) at constant NO3--N concentration (40 mgNO3--N L-1), by varying hydraulic retention time (HRT) during different trials from about 14 to 3 h. The system was able to achieve almost complete removal of nitrate (>95%) and Total Nitrogen (TN) (>92%) at NO3- loading rates between 66 and 200 gNO3--N m-3NCC d-1. The first stage reactor achieved lower values of effluent nitrate and nitrite than WHO guidelines for drinking water quality (<11.3 mg NO3--N L-1, and 0.9 mgNO2--N L-1, respectively) up to a nitrate loading rate of 167 gNO3--N m-3NCC d-1; in these conditions the second stage acted mainly as polishing step. From a loading rate of 200 gNO3--N m-3NCC d-1 on, N2O accumulation was observed in the first stage reactor, afterwards successfully removed in the second stage. Maximum nitrate removal rate of the 2-step process was 259.83 gNO3--N m-3NCC at HRT of 3.19 h. The specific energy consumption of the system (SEC) decreased with decreasing HRT, both in terms of mass of nitrate removed (SECN) and volume treated (SECV). The described combination of two bioelectrochemical systems system hence proved to be effective for groundwater denitrification.

Wastewater treatment with a new electrically enhanced biomass concentrator reactor: trial application and technological perspectives.

Biomass concentrator reactors (BCRs) are an alternative wastewater treatment technology developed as a possible solution to membrane bioreactors' (MBRs) high construction and energetic costs. BCRs are an alternative based on the same principle of biomass retention, using a coarser filter medium instead of a membrane. A BCR-derived technology enhanced by an electric field called electrically enhanced biomass concentrator reactor (E2BCR) was developed, designed, and tested for wastewater treatment at different organic loads for a period of 100 days. The electrically enhanced reactor showed better chemical oxygen demand (COD) removal performances that the non-enhanced control reactor (90% and 84%, respectively), and a lower fouling tendency. The E2BCR proved to be more energy efficient in comparison with the control reactor in terms of energy consumption per mass of COD removed.

Assessment of arsenic removal efficiency by an iron oxide-coated sand filter process.

Arsenic is among the most dangerous contaminants which can limit groundwater use for drinking water consumption. Among the most diffused As-removal technologies around the world, adsorptive media systems are usually favored for relatively low cost and simplicity of operation. This study examines the performance of a laboratory-scale iron oxide-coated sand (IOCS) column filter, to remove arsenic (arsenate (As[V]) and arsenite (As[III])) from groundwater. This technology could be adopted in small communities, as it showed consistent removal rates of 99% with an easy-to-operate process. Some considerations about the possible introduction of such technology in developing countries are provided, highlighting the general impacts to human health related to high arsenic concentrations in groundwater. This, among other adsorption processes, could be recommended as a sustainable mean of ensuring good drinking water quality in developing regions, reducing human health impacts.

Industrial wastewater treatment with a bioelectrochemical process: assessment of depuration efficiency and energy production.

Development of renewable energy sources, efficient industrial processes, energy/chemicals recovery from wastes are research issues that are quite contemporary. Bioelectrochemical processes represent an eco-innovative technology for energy and resources recovery from both domestic and industrial wastewaters. The current study was conducted to: (i) assess bioelectrochemical treatability of industrial (dairy) wastewater by microbial fuel cells (MFCs); (ii) determine the effects of the applied organic loading rate (OLR) on MFC performance; (iii) identify factors responsible for reactor energy recovery losses (i.e. overpotentials). For this purpose, an MFC was built and continuously operated for 72 days, during which the anodic chamber was fed with dairy wastewater and the cathodic chamber with an aerated mineral solution. The study demonstrated that industrial effluents from agrifood facilities can be treated by bioelectrochemical systems (BESs) with >85% (average) organic matter removal, recovering power at an observed maximum density of 27 W m-3. Outcomes were better than in previous (shorter) analogous experiences, and demonstrate that this type of process could be successfully used for dairy wastewater with several advantages.

Feedstock and process influence on biodiesel produced from waste sewage sludge.

Disposal of sewage sludge is one of the most important issues in wastewater treatment throughout Europe, as EU sludge production, estimated at 9.5 million tons dry weight in 2005, is expected to approach 13 million tons in 2020. While sludge disposal costs may constitute 30-50% of the total operation costs of wastewater treatment processes, waste sewage sludge still contains resources that may be put to use, like nutrients and energy, that can be recovered through a variety of approaches. Research has shown that waste sewage sludge can be a valuable and very productive feedstock for biodiesel generation, containing lipids (the fats from which biofuels are extracted) in amounts that would require large areas cultivated with typical biodiesel feedstock, to produce, and at a much lower final cost. Several methods have been tested for the production of biodiesel from sewage sludge. To date, among the most efficient such process is pyrolysis, and in particular Microwave-Assisted Pyrolysis (MAP), under which process conditions are more favorable in energetic and economic terms. Sludge characteristics are very variable, depending on the characteristics of the wastewater-generating service area and on the wastewater treatment process itself. Each sludge can be considered a unique case, and as such experimental determination of the optimal biodiesel yields must be conducted on a case-by-case basis. In addition to biodiesel, other pyrolysis products can add to the energetic yield of the process (and not only). This paper discusses how feedstock properties and process characteristics may influence biodiesel (and other products) yield from pyrolytic (and in particular, MAP) processes, and discusses future possible technological developments.

Comparative application of different risk assessment models and implications on resulting remediation options.

The issue of contaminated soils and their productive recovery is a quite controversial environmental and economic problem with important consequences for its social, public health and sustainability aspects. The sheer number and characteristics of the polluted sites are so large and varied, and the definition of priorities related to their remediation interventions so site-dependent, that proper characterization and final environmental quality goals reflect a strategic importance. One of the possible approaches to site specific approach and site priority ranking can be that of carrying out, respectively, absolute and comparative analysis procedures. An important aspect to be solved is represented by the necessity to consider not only the potential risk to public health, but also the best possible financial return from the investments for remediation, especially when carried out with public money. In this paper, different contaminated sites' risk assessment approaches are considered, compared and their applicability to support sustainable policies discussed using a case study.

Efficient degradation of MtBE and other gasoline-originated compounds by means of a biological reactor of novel conception: two case studies in Italy and the USA.

The presence of MtBE in groundwaters, due to its past use as an oxygenate additive to "green" gasoline, poses potential threats to human health as a possible carcinogen. As its chemical properties render it very mobile and poorly treatable by means of bioremediation, chemical oxidation, stripping, or carbon adsorption, a new, ex-situ treatment process was recently developed by the US EPA and the University of Cincinnati. The objective of the study was to evaluate the effectiveness of this pump-and-treat technology in actual contaminated groundwater plumes in the field in two different conditions. The technology based on the combination of aerobic degradation and a special filtration medium is simple to operate, easily meets the challenge of producing a highly polished effluent in a cost-effective fashion, compared to other processes.