Ag-Tech, Yuma, AZ

Overview

Ag-Tech is a biosolids management corporation that began utilizing biosolids from Yuma, Arizona.
In 1988, they expanded their operation to accept biosolids from Los Angeles.  The biosolids are spread on 8 square miles of company owned land which utilizes the biosolids as fertilizer for irrigated feed crops that are shipped mostly overseas to Japan.
 
The process design starts by dewatering to around 20% solids at the treatment plants before shipping to the application site.  Fourteen trucks a day bring the solids to the site where the biosolids are stored in 2 holding basins and reliquify to around 4% solids.  A large centrifugal pump mixes the solids and controls the solid ratios by the amount of water introduced to the lines.  The company has supplied wells on site for the water source.

The biosolids are pumped to the sites by a system of fixed and movable pipes.  The sludge is applied with a tractor-mounted injector.  The application is done in a triple crosshatch pattern to distribute the sludge uniformly.  The triple crosshatch system pattern injects the first time and then again at 90 degrees to the first application.  After the first two applications, the third application is at 45 degrees to the second.  This is similar to the pattern used to cut most athletic grass fields.  The average rate of application is approximately 7 dry tons per acre.

Ag-tech owns roughly 10,000 to 11,000 acres divided up into 47 plots.  On these plots they grow barley, wheat, and alfalfa for feed and some cotton.  Most of these crops are exported to Japan for resale.
 

Monitoring

Wastewater:
The wastewater is monitored at the treatment plants frequently and is given an identification number which is sent to the computer database in Yuma.  The number, location, time of the loading, and the weight of the load are all stored in the database for up to the minute reports taken in Yuma.  Ag-Tech also collects random grab samples of the solids to check its monitoring database for errors.

Soils and Crops:
Soil samples are taken before and after the applications at all sites.  Plant samples are collected at harvest time and monitored for metal concentration and yield.  These are compared to plants grown without using the biosolid application.  The soil and crop samples are cataloged for future comparison or if any problem should arise.
 

Results:

The biosolids collected in Los Angeles were tested for 6 metal concentrations. The following table shows the results of these tests.
 
 

The 1991 levels are below the pollution control limits set out in 40 CFR part 503.

Here in Yuma, the climate is arid and water conservation is a major priority.  The water use on the amended soils is 26% lower than on non amended soils.  The yields on the biosolid amended soils were 10 to 85 % higher than fields receiving just fertilizer and 29 to 288 % higher than yields on unfertilized soils.  Alfalfa seeds showed the lowest responses to biosolids while  hay crops respond the best.

Overall, the application has improved the crop production in Yuma.  The low rainfall rates limit mobility of the biosolids.  The one negative aspect seen here was the increased frost possibilities due to the increased soil moisture levels recorded during the first and last frosts of the year.
 

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