Jaime Nivala

Clogging in subsurface-flow treatment wetlands: measurement, modeling and management.

This paper reviews the state of the art in measuring, modeling, and managing clogging in subsurface-flow treatment wetlands. Methods for measuring in situ hydraulic conductivity in treatment wetlands are now available, which provide valuable insight into assessing and evaluating the extent of clogging. These results, paired with the information from more traditional approaches (e.g., tracer testing and composition of the clog matter) are being incorporated into the latest treatment wetland models. Recent finite element analysis models can now simulate clogging development in subsurface-flow treatment wetlands with reasonable accuracy. Various management strategies have been developed to extend the life of clogged treatment wetlands, including gravel excavation and/or washing, chemical treatment, and application of earthworms. These strategies are compared and available cost information is reported.

Hydraulic characterization and optimization of total nitrogen removal in an aerated vertical subsurface flow treatment wetland.

In this study, a side-by-side comparison of two pilot-scale vertical subsurface flow constructed wetlands (6.2 m(2)×0.85 m, q(i)=95 L/m(2) d, τ(n)=3.5 d) handling primary treated domestic sewage was conducted. One system (VA-i) was set to intermittent aeration while the other was aerated continuously (VAp-c). Intermittent aeration was provided to VA-i in an 8 h on/4 h off pattern. The intermittently aerated wetland, VA-i, was observed to have 70% less nitrate nitrogen mass outflow than the continuously aerated wetland, VAp-c. Intermittent aeration was shown to increase treatment performance for TN while saving 33% of running energy cost for aeration. Parallel tracer experiments in the two wetlands showed hydraulic characteristics similar to one Continuously Stirred Tank Reactor (CSTR). Intermittent aeration did not significantly affect the hydraulic functioning of the system. Hydraulic efficiencies were 78% for VAp-c and 76% for VA-i.

Reversing clogging in subsurface-flow constructed wetlands by hydrogen peroxide treatment: two case studies

One of the most frequently encountered operational problems in subsurface-flow constructed wetlands is clogging. Traditionally, the restoration procedure is to remove the clogged gravel or sand and replace it with clean material. This method, while effective, is costly and may require sections of the facility to be taken offline for extended periods of time. Another common remediation strategy is to have a resting period for each wetland cell, although this is not an option for very small systems which often consist of only one treatment cell. Recently, a more radical approach has been tested on a number of lab-scale and pilot-scale setups which consists of an aggressive oxidation of organic matter by means of hydrogen peroxide (H(2)O(2)). Results indicate that after treatment, clogging was substantially reduced and that H(2)O(2) did not appear to have a long-term negative effect on plants and biofilms. The outcomes of two full-scale tests are discussed in this paper.

Emerging organic contaminants in vertical subsurface flow constructed wetlands: Influence of media size, loading frequency and use of active aeration

Four side-by-side pilot-scale vertical flow (VF) constructed wetlands of different designs were evaluated for the removal of eight widely used emerging organic contaminants from municipal wastewater (i.e. ibuprofen, acetaminophen, diclofenac, tonalide, oxybenzone, triclosan, ethinylestradiol, bisphenol A). Three of the systems were free-draining, with one containing a gravel substrate (VGp), while the other two contained sand substrate (VS1p and VS2p). The fourth system had a saturated gravel substrate and active aeration supplied across the bottom of the bed (VAp). All beds were pulse-loaded on an hourly basis, except VS2p, which was pulse-loaded every 2h. Each system had a surface area of 6.2m(2), received a hydraulic loading rate of 95 mm/day and was planted with Phragmites australis. The beds received an organic loading rate of 7-16 gTOC/m(2)d. The sand-based VF (VS1p) performed significantly better (p<0.05) than the gravel-based wetland (VGp) both in the removal of conventional water quality parameters (TSS, TOC, NH4-N) and studied emerging organic contaminants except for diclofenac (85 ± 17% vs. 74 ± 15% average emerging organic contaminant removal for VS1p and VGp, respectively). Although loading frequency (hourly vs. bi-hourly) was not observed to affect the removal efficiency of the cited conventional water quality parameters, significantly lower removal efficiencies were found for tonalide and bisphenol A for the VF wetland that received bi-hourly dosing (VS2p) (higher volume per pulse), probably due to the more reducing conditions observed in that system. However, diclofenac was the only contaminant showing an opposite trend to the rest of the compounds, achieving higher elimination rates in the wetlands that exhibited less-oxidizing conditions (VS2p and VGp). The use of active aeration in the saturated gravel bed (VAp) generally improved the treatment performance compared to the free-draining gravel bed (VGp) and achieved a similar performance to the free-draining sand-based VF wetlands (VS1p).

Nitrification cessation and recovery in an aerated saturated vertical subsurface flow treatment wetland: Field studies and microscale biofilm modeling.

In aerated treatment wetlands, oxygen availability is not a limiting factor in sustaining a high level of nitrification in wastewater treatment. In the case of an air blower failure, nitrification would cease, potentially causing adverse effects to the nitrifying bacteria. A field trial was completed investigating nitrification loss when aeration is switched off, and the system recovery rate after the aeration is switched back on. Loss of dissolved oxygen was observed to be more rapid than loss of nitrification. Nitrate was observed in the effluent long after the aeration was switched off (48h+). A complementary modeling study predicted nitrate diffusion out of biofilm over a 48h period. After two weeks of no aeration in the established system, nitrification recovered within two days, whereas nitrification establishment in a new system was previously observed to require 20-45days. These results suggest that once established resident nitrifying microbial communities are quite robust.

Effect of design and operational conditions on the performance of subsurface flow treatment wetlands: Emerging organic contaminants as indicators

Six pilot-scale subsurface flow treatment wetlands loaded with primary treated municipal wastewater were monitored over one year for classical wastewater parameters and a set of emerging organic compounds (EOCs) serving as process indicators for biodegradation: caffeine, ibuprofen, naproxen, benzotriazole, diclofenac, acesulfame, and carbamazepine. The wetland technologies investigated included conventional horizontal flow, unsaturated vertical flow (single and two-stage), horizontal flow with aeration, vertical flow with aeration, and reciprocating. Treatment efficiency for classical wastewater parameters and EOCs generally increased with increasing design complexity and dissolved oxygen concentrations. The two aerated wetlands and the two-stage vertical flow system showed the highest EOC removal, and the best performance in warm season and most robust performance in the cold season. These three systems performed better than the adjacent conventional WWTP with respect to EOC removal. Acesulfame was observed to be removed (>90%) by intensified wetland systems and with use of a tertiary treatment sand filter during the warm season. Elevated temperature and high oxygen content (aerobic conditions) proved beneficial for EOC removal. For EOCs of moderate to low biodegradability, the co-occurrence of aerobic conditions and low content of readily available carbon appears essential for efficient removal. Such conditions occurred in the aerated systems and with use of a tertiary treatment sand filter.

Community-Level Physiological Profiling of Microbial Communities in Constructed Wetlands: Effects of Sample Preparation

Community-level physiological profiling (CLPP) using BIOLOG® EcoPlates™ has become a popular method for characterizing and comparing the functional diversity, functional potential, and metabolic activity of heterotrophic microbial communities. The method was originally developed for profiling soil communities; however, its usage has expanded into the fields of ecotoxicology, agronomy, and the monitoring and profiling of microbial communities in various wastewater treatment systems, including constructed wetlands for water pollution control. When performing CLPP on aqueous samples from constructed wetlands, a wide variety of sample characteristics can be encountered and challenges may arise due to excessive solids, color, or turbidity. The aim of this study was to investigate the impacts of different sample preparation methods on CLPP performed on a variety of aqueous samples covering a broad range of physical and chemical characteristics. The results show that using filter paper, centrifugation, or settling helped clarify samples for subsequent CLPP analysis, however did not do so as effectively as dilution for the darkest samples. Dilution was able to provide suitable clarity for the darkest samples; however, 100-fold dilution significantly affected the carbon source utilization patterns (CSUPs), particularly with samples that were already partially or fully clear. Ten-fold dilution also had some effect on the CSUPs of samples which were originally clear; however, the effect was minimal. Based on these findings, for this specific set of samples, a 10-fold dilution provided a good balance between ease of use, sufficient clarity (for dark samples), and limited effect on CSUPs. The process and findings outlined here can hopefully serve future studies looking to utilize CLPP for functional analysis of microbial communities and also assist in comparing data from studies where different sample preparation methods were utilized.

Application of cell-based bioassays to evaluate treatment efficacy of conventional and intensified treatment wetlands

Constructed wetlands are commonly used for wastewater treatment when centralized sewage treatment is not feasible. Many studies have focused on the removal of micropollutants by treatment wetlands, but little is known about how well they can remove biological activity. Here we studied the removal efficacy of conventional and intensified treatment wetland designs using both chemical analysis of conventional wastewater parameters and treatment indicator chemicals (caffeine, ibuprofen, naproxen, benzotriazole, diclofenac, acesulfame, carbamazepine) as well as a panel of in vitro bioassays indicative of different stages of cellular toxicity pathways, such as xenobiotic metabolism, receptor-mediated effect and adaptive stress responses. Water samples collected before and after seven treatment wetlands were compared against the adjacent municipal wastewater treatment plant. The intensified treatment wetlands generally removed micropollutants and biological activity to a greater extent than the conventional wastewater treatment plant, whereas the conventional horizontal subsurface flow wetland showed poor removal of all indicators. Carbamazepine was not well removed by any of the studied systems as expected from reported recalcitrance in aerobic environments. Estrogenic activity, which is a commonly used biological endpoint indicator for wastewater treatment, was removed very well by the intensified wetlands (97 to 99.5%) with similar or slightly lower removal efficacy for all other biological endpoints. The results highlight the importance of applying indicator bioassays complementary to indicator chemical analysis for monitoring treatment efficacy. The high removal efficacy of biological effects as a measure of total effect-scaled concentrations of chemicals provides further support to the use of intensified wetlands for wastewater treatment.

Emerging Biodegradation of the Previously Persistent Artificial Sweetener Acesulfame in Biological Wastewater Treatment

The persistence of acesulfame (ACE) in wastewater treatment (and subsequently the aquatic environment) has led to its use as a marker substance for wastewater input into surface water and groundwater. However, ACE degradation of >85% during summer and autumn was observed in nine German wastewater treatment plants (WWTPs). Annual removal performance was more stable in larger plants, enhanced by low biological oxygen demand and impeded by water temperatures below 10 °C. Literature data suggest that the potential to degrade ACE emerged in WWTPs around the year 2010. This development is ongoing, as illustrated by ACE content in the German rivers Elbe and Mulde: Between 2013 and 2016 the ACE mass load decreased by 70-80%. In enrichment cultures with ACE as sole carbon source the carbonaceous fraction of ACE was removed completely, indicating catabolic biotransformation and the inorganic compound sulfamic acid formed in quantitative amounts. Sequencing of bacterial 16S rRNA genes suggests that several species are involved in ACE degradation, with proteobacterial species affiliated to Phyllobacteriaceae, Methylophilaceae, Bradyrhizobiaceae, and Pseudomonas becoming specifically enriched. ACE appears to be the first micropollutant for which the evolution of a catabolic pathway in WWTPs has been witnessed. It can yet only be speculated whether the emergence of ACE removal in WWTPs in different regions of the world is due to independent evolution or to global spreading of genes or adapted microorganisms.

Statistical Analysis of Treatment Performance in Aerated and Nonaerated Subsurface Flow Constructed Wetlands

This study compares the treatment performance of aerated and nonaerated horizontal flow constructed wetlands. Results are presented in a series of performance charts that relate effluent concentrations to influent mass loadings. A statistical approach has been developed that allows the application of confidence intervals to system performance. Performance data is presented for predicted median (50th-percentile) and 90th-percentile effluent concentrations. Aeration was found to improve removal of biochemical oxygen demand (BOD), total suspended solids (TSS), and to a lesser extent, total Kjeldahl nitrogen (TKN). Benefits of aeration include lower median effluent concentrations at a given influent mass loading, less variability in effluent quality, and lower background concentrations (C*). In contrast, aeration was observed to have no impact on total phosphorus (TP) or fecal coliform bacteria removal.