Water quality and hydraulic performance of biochar amended biofilters for management of agricultural runoff

This research evaluated the effect of biochar amendment rate on nitrogen species and organic carbon removals and hydraulic performance in biofilter columns treating dairy farm runoff. Initial studies compared the performance of sand columns amended with two types of biochar with different specific surface area (SA) and cation exchange capacity (CEC) with an un-amended sand column. The results showed that biochar enhanced N-species removal due to its unique physicochemical properties. In subsequent tests, two biofilter columns with different biochar fractions (20% and 50% by volume) were operated at varying hydraulic loading rates and antecedent dry conditions. Total nitrogen, ammonia, organic nitrogen and organic carbon removals were significantly higher in the column with the higher biochar fraction. The high CEC of biochar increased ammonium retention during the application period, allowing for nitrification during the antecedent dry periods (ADPs) when aerobic conditions developed in the media pores. High biochar SA also resulted in greater retention of DON and DOC by adsorption. A variable saturation flow model of biochar amended biofiltration was developed using HYDRUS-1D software. The model was calibrated using data from conservative tracer and moisture content studies. Model results showed that the high microporous structure of the biochar increases the time needed to reach full saturation, lowers the saturated conductivity and increases the hydraulic retention time in the medium. This calibrated model can be used to design field scale biofilter systems for managing agricultural runoff.

Hindcasting multidecadal predevelopment groundwater levels in the Floridan aquifer

Establishing predevelopment benchmark groundwater conditions is challenging without long-term records to discern impacts of pumping and climate change on aquifer levels. Understanding periodic natural cycles and trends require 100 years or more data which rarely exist. Using limited records, we develop an approach to hindcast multidecadal levels and examine the temporal evolution of climatic and pumping impacts. The methodology includes a wavelet-aided statistical model, constrained by temporal scales of physical processes responsible for groundwater level variation, including rainfall, evapotranspiration and pumping stresses. The model and hindcasts are tested at three sites in Florida using traditional split calibration-verification methods for the period of record and with the documented historical drought and wet years for the period of no-record. The pumping impact is quantified over time and compared with regional groundwater models, revealing that withdrawals are responsible for 30 to 70% of the declines in levels since 1960s. Hindcasting yielding 110 years of monthly levels is used to assess the effect of climate change and pumping on the frequency of critical low levels. At all three sites, the frequencies of critical low levels increase significantly in the 1960 to 2015 period when compared to the 1904 to 1959 period. For example, at site 1, the return period of the critical low level is shortened by 3.9 years due to climate change and 2.2 years due to pumping.

Biochar amendment of stormwater bioretention systems for nitrogen and Escherichia coli removal: Effect of hydraulic loading rates and antecedent dry periods

Bioretention systems improve stormwater infiltration and water quality; however, limited total nitrogen (TN) and fecal indicator bacteria (FIB) removal is observed in sand-based bioretention media. In this study, the fate of nitrogen and E. coli in bioretention systems was investigated through batch and column studies using sand media, with and without biochar addition. Variables investigated included biochar characteristics, hydraulic loading rate (HLR) and antecedent dry period (ADP). Total ammonia nitrogen (TAN), dissolved organic carbon (DOC), and E. coli removals were significantly higher in biochar-amended columns due to biochar's high cation exchange capacity and specific surface area. TAN adsorption resulted in increased nitrification during the ADP when aerobic conditions developed. Moisture content data revealed that saturated conditions prevailed toward the bottom of biochar-amended columns for several days, favoring denitrification and TN removal. Biochar amended columns also showed more stable TAN, DOC and E. coli effluent concentrations under varying HLR and ADP.

Evaluation of ground water monitoring network by principal component analysis

Principal component analysis is a data reduction technique used to identify the important components or factors that explain most of the variance of a system. This technique was extended to evaluating a ground water monitoring network where the variables are monitoring wells. The objective was to identify monitoring wells that are important in predicting the dynamic variation in potentiometric head at a location. The technique is demonstrated through an application to the monitoring network of the Bangkok area. Principal component analysis was carried out for all the monitoring wells of the aquifer, and a ranking scheme based on the frequency of occurrence of a particular well as principal well was developed. The decision maker with budget constraints can now opt to monitor principal wells which can adequately capture the potentiometric head variation in the aquifer. This was evaluated by comparing the observed potentiometric head distribution using data from all available wells and wells selected using the ranking scheme as a guideline.