In situ treatment technologies for pit latrines to mitigate groundwater contamination by fecal pathogens: a review of recent technical advances

On-site sanitation systems such as pit latrines are extensively used around the world, while there is a growing number of evidence documenting the impact of pit latrines on groundwater quality that may affect human health. Hence, this paper summarizes the various safe-sanitation technologies by broadly categorizing them into fecal pathogen disinfection methods (anaerobic digestion, chemical disinfection, biological additives, solar pasteurization and vermicomposting) and capturing methods (pit lining and permeable reactive barriers, the latter of which simultaneously capture and sanitize fecal sludge in pit latrines). While some of the reviewed technologies have been widely practiced for mitigating microbial contamination of the groundwater, others are still in the early stage of commercialization and field validation. Though there are challenges to the selection and adoption of the most appropriate technology, this paper discusses the readiness of each technology as a stand-alone fecal sludge management solution.

A bibliometric analysis of permeable reactive barrier enhanced electrokinetic treatment for sustainable polluted soil remediation

Research on soil remediation continues to develop, one of which is electrokinetic remediation combined with a permeable reactive barrier as a medium to prevent the migration of metals removed from the anode and cathode spaces. Thus, it is hoped that there is no need for reprocessing the residue resulting from electrokinetic remediation. This study aims to conduct a bibliographical analysis related to electrokinetic remediation coupled by permeable reactive barriers for heavy metal contaminated soil and to examine the effect of using various types of reactive barrier materials and their placement on the pollutants removal in the soil. Based on the results of bibliographic analysis, 26 relevant scientific articles were obtained, and the most publications in 2020 with 27% additional article publications are found. China and Environmental Science and Pollutant Research are the countries and journals that contribute the most to publications related to EK-PRB on heavy metal polluted soils.

Effects of Contact Time and Flow Configuration on the Acid Mine Drainage Remediation Capabilities of Pervious Concrete

This paper investigates the Acid Mine Drainage (AMD) remediation capabilities of pozzolanic pervious concrete Permeable Reactive Barriers (PRBs) with a specific focus on the effects of flow configuration and contact time on the remediation efficiency. Raw AMD was collected from an abandoned coal mine. Two flow configurations, gravity flow and column flow, were tested at a laboratory scale with gradually increasing contact times. The gravity flow configuration with two orders of magnitude less liquid-concrete contact time achieved AMD treated water quality equivalent to the high retention column flow configuration. Concentrations of iron, aluminium, sulphate, magnesium and sodium were reduced by more than 99%, 80%, 17%, 22% and 20%, respectively, at the tested limits while calcium and potassium concentrations were increased by up to 16% and 300%, respectively. The study findings indicate that the lifecycle costs of pervious concrete PRBs can be significantly reduced when the PRBs are operated under gravity flow.

A Comprehensive Review for Groundwater Contamination and Remediation: Occurrence, Migration and Adsorption Modelling

The provision of safe water for people is a human right; historically, a major number of people depend on groundwater as a source of water for their needs, such as agricultural, industrial or human activities. Water resources have recently been affected by organic and/or inorganic contaminants as a result of population growth and increased anthropogenic activity, soil leaching and pollution. Water resource remediation has become a serious environmental concern, since it has a direct impact on many aspects of people’s lives. For decades, the pump-and-treat method has been considered the predominant treatment process for the remediation of contaminated groundwater with organic and inorganic contaminants. On the other side, this technique missed sustainability and the new concept of using renewable energy. Permeable reactive barriers (PRBs) have been implemented as an alternative to conventional pump-and-treat systems for remediating polluted groundwater because of their effectiveness and ease of implementation. In this paper, a review of the importance of groundwater, contamination and biological, physical as well as chemical remediation techniques have been discussed. In this review, the principles of the permeable reactive barrier’s use as a remediation technique have been introduced along with commonly used reactive materials and the recent applications of the permeable reactive barrier in the remediation of different contaminants, such as heavy metals, chlorinated solvents and pesticides. This paper also discusses the characteristics of reactive media and contaminants’ uptake mechanisms. Finally, remediation isotherms, the breakthrough curves and kinetic sorption models are also being presented. It has been found that groundwater could be contaminated by different pollutants and must be remediated to fit human, agricultural and industrial needs. The PRB technique is an efficient treatment process that is an inexpensive alternative for the pump-and-treat procedure and represents a promising technique to treat groundwater pollution.

Modified Zeolite as Purification Material in Wastewater Treatment: A Review

Natural zeolite is a hydrated aluminosilicate substance that has excellent ion exchange and adsorption properties and is environmentally and economically friendly. This review describes the current application and modification of zeolite in wastewater treatment using acid and surfactants, zeolite composites (such as zeolite membranes), permeable reactive barriers and photocatalysts. The properties of zeolite as well as the regeneration and desorption of cast-off zeolite are briefly reviewed. Modifications are made to improve the capability of zeolite in wastewater treatment facilities. Furthermore, this review proposes the integration of zeolite and other available technologies to treat emerging pollutants in wastewater. Different types of zeolite (natural and synthetic zeolite of different origins) are compared, and their properties are evaluated. Different type of pollutants and treatment methods involving zeolite are also discussed. Zeolite is enhanced to solve the problem of various pollutants in wastewater.

Modeling porosity loss in Fe0-based permeable reactive barriers with Faraday’s law

Solid iron corrosion products (FeCPs), continuously generated from iron corrosion in Fe0-based permeable reactive barriers (PRB) at pH > 4.5, can lead to significant porosity loss and possibility of system’s failure. To avoid such failure and to estimate the long-term performance of PRBs, reliable models are required. In this study, a mathematical model is presented to describe the porosity change of a hypothetical Fe0-based PRB through-flowed by deionized water. The porosity loss is solely caused by iron corrosion process. The new model is based on Faraday’s Law and considers the iron surface passivation. Experimental results from literature were used to calibrate the parameters of the model. The derived iron corrosion rates (2.60 mmol/(kg day), 2.07 mmol/(kg day) and 1.77 mmol/(kg day)) are significantly larger than the corrosion rate used in previous modeling studies (0.4 mmol/(kg day)). This suggests that the previous models have underestimated the impact of in-situ generated FeCPs on the porosity loss. The model results show that the assumptions for the iron corrosion rates on basis of a first-order dependency on iron surface area are only valid when no iron surface passivation is considered. The simulations demonstrate that volume-expansion by Fe0 corrosion products alone can cause a great extent of porosity loss and suggests careful evaluation of the iron corrosion process in individual Fe0-based PRB.

Comparison of Nitrogen Treatment by Four Onsite Wastewater Systems in Nutrient-Sensitive Watersheds of the North Carolina Coastal Plain

Wastewater may be a source of nitrogen (N) to groundwater and surface waters if not effectively treated. In North Carolina, onsite wastewater systems (OWSs) are used by 50% of the population for wastewater treatment, but most OWSs are not routinely monitored. There is a lack of information regarding the N contributions from OWSs to water resources. Four sites with OWSs were instrumented with groundwater wells near their drainfield trenches to compare N concentrations in groundwater to concentrations in wastewater and to determine the N treatment efficiency of the systems. Two OWSs (Site 200 and 300) were less than 1 year old, and two (Site 100 and 400) were more than 10 years old at the start of the study. Two OWSs (Site 100 and 200) used pressure dosing, while two OWSs (Site 300 and 400) used gravity distribution. The mean N treatment efficiency of the four OWSs was 77%. The new OWSs were more efficient (92%) relative to the older OWSs (62%) at reducing N concentrations. Similar N treatment efficiencies were observed when pooling data for the pressure dosed (77%) and gravity (79%) OWSs. Each OWS influenced groundwater by causing increases in N concentrations. It is important that new OWSs are installed at a shallow depth and with sufficient separation to groundwater to promote the aerobic treatment of wastewater. Remediation strategies including the installation of permeable reactive barriers or the use of media filters may be needed in some areas to reduce N transport from existing OWS.