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Field Demonstration of the Performance of the L4DB® Microbial Treatment System to Reduce Phosphorus and Other Substances from Dairy Lagoon Effluent

S. Mukhtar, S. Rahman, L. Gregory

Two upper North Bosque River segments were designated as impaired in 1998 due to point source and nonpoint source (NPS) pollution of phosphorus (P) to 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 Clean Water Act (Section 319(h)), a new technologies demonstration project was funded by the 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.L4DB® microbial treatment system) was evaluated, which may aid dairy farmers in reducing P from lagoon effluent. In many cases, this effluent is applied to waste application fields (WAFs) as irrigation water; thus reducing P in the effluent can have a direct impact on NPS pollution in the watershed.

Beginning in May 2006 a dairy’s anaerobic lagoon was treated with L4DB® microbes at an average application rate of 65 gallons (246 L) of microbial solution/month for a period of 12 months. Lagoon samples were collected monthly or bi-monthly from two different profiles: lagoon supernatant (LS, sampled from top of the liquid level to 2ft (61 cm) 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, 30 samples (3 samples per location × 10 locations) were collected during each sampling event. A set of 15 LP and 15 LS samples were mixed separately to get two composites of each for nutrients including P, solids, pH, conductivity and metals. In addition, 60 samples of lagoon effluent (hereafter IR) used to irrigate a nearby pasture were collected bi-monthly from a riser located just upstream from the big gun irrigation unit. Fifteen IR subsamples were grouped together to get four IR composite samples. The IR composite samples were also analyzed for the above mentioned physical and chemical constituents.

L4DB® microbial treatment reduced average sludge depth by 24% as compared to its pre-treatment level (however, this reduction was 16%, when sludge measurement anomaly in August 2006 was excluded). The microbial treatment also reduced averaged total solids (TS) and total suspended solids (TSS) by 43 and 45%, respectively, for the LP, and 60 and 71%, respectively, for LS. Conversely, these values increased by 124% for IR effluent over times.

This microbial treatment system was effective in reducing average total phosphorus (TP) by 27 and 52% for the LP and LS, respectively, but not effective in reducing TP concentration for IR effluent. Overall, no clear soluble reactive phosphorus (SRP) reduction trends were observed for any sampling locations. Similar to the effect on TP, the L4DB® treatment was effective in reducing total Kjeldahl nitrogen (TKN) from the LP (36%) and LS (48%), but not effective in reducing potassium (K) for LP and LS. No clear trend of reducing these nutrients from IR effluent was observed over time.

This microbial treatment system was effective in reducing metals concentration as well. The average concentration reductions of Al, Ca, Cu, Fe, and Mn for LP were over 50%, while the reduction seen in Mg was only 22%. Similarly, the concentration reductions observed in LS samples were over 60% for the same suite of elements while Mg was reduced by about 42%. No clear metal concentration reduction trends were observed for IR effluent. As a result, it can be inferred that most of these solids, nutrients, and metal reductions were likely due to microbial treatment, dilution of lagoon slurry by excessive rain and runoff as well as settling of dead and degraded bacterial mass accumulated at the bottom of lagoon. Additional measurements of lagoon sludge accumulation rate and constituents are warranted to assess possible increase in nutrients and solids due to accelerated solids settling and increased accumulation of microbial mass at the lagoon bottom.

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