Field Demonstration of the Performance of Wastewater Treatment Solution (WTS®) to Reduce Phosphorus and other Substances from Dairy Lagoon Effluent
S. Mukhtar, S. Rahman, L. Gregory
In 1998 two upper North Bosque River segments were designated as impaired due to point source and nonpoint source (NPS) pollution of phosphorus (P) in these segments of the watershed. As a result, two Total Maximum Daily Loads (TMDLs) were applied, which called for the reduction of annual loading and annual average soluble reactive P (SRP) concentrations by about 50%. Under the Clean Water Act (Section 319(h)), a new technologies demonstration project was funded by the U. S. Environmental Protection Agency (USEPA) Region 6 and administered by the Texas State Soil and Water Conservation Board (TSSWCB) for reducing water pollution associated with dairy animal production systems. As part of this demonstration, the efficacy of a prospective new technology (i.e. wastewater treatment solution, WTS®) was evaluated, which may assist dairy farmers in reducing P from lagoon effluent. In many cases, this effluent is applied to waste application fields (WAF) as irrigation water. Therefore, reducing P in the effluent can have a direct impact on NPS pollution in the watershed.
Before treating a dairy’s anaerobic lagoon with WTS® and an oxygenating additive, O2T, three separate background (pre-treatment) samplings were conducted to gather baseline information on nutrients (e.g., total phosphorus [TP], soluble reactive phosphorus [SRP], and total Kjeldahl nitrogen [TKN]) and solids (e.g., total solids [TS], total suspended solids [TSS], total dissolved solids [TDS]) data prior to inoculation. Following the third pre-treatment sampling in September 2007, the anaerobic lagoon was treated with WTS® at an averaged application rate of 1 gallon/head as a start-up. Thereafter, WTS® was applied at a rate of 0.5 gal/100 head-day (based on 600 heads), while O2T was applied at a rate of 0.1 gal/100 head-day (based on 600 heads). To mimic the repeatability of lagoon treatment, two large tanks were filled with untreated flushed manure to assess the treatment effect on flushed manure from free-stall. Tank 1 (T1) was treated manually on a monthly basis, with WTS® at a rate of 16 oz (0.5 L) and with O2T at a rate of 7 oz (0.25 L) and Tank 2 (T2) was used as the control (no treatment was applied).
Following treatment, lagoon samples were collected monthly or bi-monthly from two different profiles: lagoon supernatant (LS), sampled from the top of the liquid level to 2 ft (0.61 m) depth and lagoon profile (LP), sampled from the entire depth of the lagoon using a sludge judge (a sampling tube with a check valve at the bottom to take lagoon sample at different depths). For each LP and LS, 27 samples (3 samples per location × 9 locations) were collected during each sampling event. A set of 9 LP and 9 LS samples were mixed separately to get two composites of each for nutrients including P, solids, pH, conductivity and metals. Similarly, samples were collected from tank supernatant (1 ft or 0.30 m below liquid surface) and profile (from the entire depth of the tank) in each sampling event. During each sampling event, a total 36 (9 samples per tank × 2 tanks × 2 profiles) samples were collected from the two tanks. Each set of 9 tank supernatant and 9 tank profile sample bottles were mixed separately to get two tank supernatant (T1S and T2S) and two tank profile (T1P and T2P) composite samples of each for analysis.
WTS® treatment was somewhat effective in reducing sludge depth by 10% compared to its pre-treatment level. This reduction of sludge depth was due to microbial treatment, which will likely improve lagoon effluent characteristics, increase lagoon capacity and reduce maintenance cost for this lagoon. This treatment system increases pH in the LS significantly as compared to LP. Similar to lagoon pH, the treated tank T1 had a slightly higher pH as compared to untreated tank T2 in both tank profiles, although differences were not statistically significant. There was no significant reduction in TS either in lagoon or tank environments due to WTS® treatment. Overall TSS was reduced by 7% and 9% for LP and LS, respectively, when concentrations of these parameters averaged across post-treatment events were compared with the averages across pre-treatment events. There were no differences in TSS concentrations of treated and untreated tank samples at either LS or LP. Following microbial treatment of the lagoon, TDS concentration both in LS and LP increased, although no significant differences were observed between the two profiles. Overall, the TDS concentration in LS was 13% higher than that of LP.
There was not a significant reduction in TP in either lagoon sampling profile. TP concentration in the treated tank profile was reduced by 17%, yet increased by 2% in the untreated tank profile samples. However, TP reduction values for treated and untreated tank supernatant samples were 60 and 55%, respectively. This suggested that the differences in TP reduction between treated and untreated samples were due to treatment effects. SRP concentration in both LP and LS samples increased gradually, although differences were not significant between LP and LS. A similar SRP increasing trend was also observed for tank samples, but differed in that the treated tank had a higher SRP concentration than that of untreated tank samples, due to greater TDS in tank supernatant. TKN in LP and LS reduced by 29 and 19%, respectively, but a greater TKN reduction was observed in tank profile (60 and 47% in treated and untreated tank profile samples, respectively) and tank supernatant samples (88 to 86% in treated and untreated tank supernatant samples, respectively) as compared to lagoon samples. Following the microbial treatment, the conductivity and potassium (K) concentration increased in both profiles of the lagoon and treated tank (T2). Three chemical quality parameters indicate the effectiveness of a wastewater treatment system such as biological oxygen demand (BOD), suspended solids, and TP (van Loon and Duffy 2000). Suspended solids and TP were both monitored in this study and had insignificant variation between pre-treatment and post-treatment. The purpose of this study was to evaluate the effectiveness of WTS® in reducing P and other substances from lagoon effluent to be applied to WAFs. Therefore, this treatment system was not very effective in reducing phosphorus and other nutrients from the lagoon effluent, especially soluble parameters. Conclusions indicate that more studies are needed to assess the effectiveness of this treatment over a longer time period.