Agricultural use suitability assessment and characterization of municipal liquid sludge: Based on South Africa survey.

Sludge recycling as an agricultural resource has gained great attention worldwide. This is exacerbated by the ever-rising municipal wastewater production and the realization of its potential as a soil amendment resource. Sludge suitability assessment and characterization is crucial to prompt informed decisions regarding its use on agricultural lands. Liquid sludge samples were collected from eighteen wastewater treatment plants (WWTPs) employing three different treatment processes in South Africa. Samples were analysed for physical and chemical parameters. Sludges' pH ranged from 4.5-9.5. Heavy metals concentrations were below the threshold level except for two waste activated sludge (WAS) which were downgraded to class B due to high Lead (Pb) content. Two anaerobically digested (AnD) sludges were downgraded to classes B and C because of high Pb and Cadmium (Cd) concentrations respectively. Electrical conductivity (EC) was above the 200 mS m-1 threshold in AnD and in one of aerobically digested (AeD) sludges whilst WAS had ≤100 mS m-1. Nitrogen (N): Phosphorus (P) ratios of the sludges were <8. Application of biosolids with low N:P ratio based on crop N requirements would lead to P pollution. Sustainable sludge application options were either to apply dry sludge based on crop N or P requirements and supplement the nutrient deficit with other fertilizer sources. The use of current liquid sludge as irrigation water to meet crop water needs and or applying dry sludge at 10 tons ha-1 options showed that such options are unsustainable and would add excess nutrients above crop need which would result in agroecosystems pollution. The study findings suggest that, supposedly these liquid sludges are used for irrigation, they should be diluted with fresh water or deficit irrigation should be implemented to limit nutrient load.

Characterization of fresh yard trimmings for agricultural use.

Direct application of yard trimmings to agricultural land can benefit soils and crop production, while providing an outlet for handling high volumes of materials at compost facilities. Variability in the composition of yard trimmings can make it difficult to determine appropriate application rates. Our objective was to characterize the chemical composition and variability of yard trimmings generated throughout the spring and summer season at facilities in the Puget Sound region of Washington State. Yard trimmings were sampled from four composting facilities on five dates between April and August 1999. One material contained mostly grass clippings and had higher mean total N (3.2%) than mixed grass and woody materials (1.5-2%). Mean C:N was lower in the grass-rich material (12:1 vs. 15 to 21:1), while mean ammonium concentrations were similar (0.18-0.28%). Variation among facilities was greater than variation over time. The amount of variation observed with other nutrients, pH, EC, or trace elements would not affect use of the yard trimmings in agriculture. Our results suggest that it is possible to characterize yard trimmings adequately for agricultural use.

Seven years of biosolids versus inorganic nitrogen applications to tall fescue.

Repeated applications of municipal wastewater biosolids is cost effective for biosolids managers, but may lead to undesirable accumulations of nutrients or contaminants. We evaluated the effects of seven years of biosolids applications on tall fescue (Festuca arundinacea Schreb.) production and nutrient availability. We compared two types of Class A biosolids applied to tall fescue on a sandy loam in western Washington. Mean annual biosolids rates of 290, 580, and 870 kg total N ha(-1) yr(-1) were compared with inorganic N and zero-N controls using a randomized complete block design. We measured yield and N uptake for each forage harvest, plant tissue metals at selected harvests, soil nitrate each fall, diethylenetriaminepentaacetic acid (DTPA)-extractable metals after five years of applications, and soil pH, available P, and organic C after seven years. Forage yields increased with biosolids rate. Apparent nitrogen recovery (ANR) for biosolids averaged 18% in 1993 (Year 1), 35% in 1994, and 46% in 1999. The ANR for inorganic N averaged 62% from 1994-1999. Residual soil nitrate was less than 25 kg ha(-1) for all treatments through 1995, but increased beginning in 1996 for the high biosolids rate. Biosolids increased soil organic C levels by 2 to 5 g kg(-1) and Bray-1 P levels by 300 to 600 mg kg(-1) (0-15 cm depth). Plant tissue Zn increased from 24 to 66 mg kg(-1) at the highest application rate. Nearly all of the DTPA-extractable metals remained in the 0- to 8-cm soil depth.

Simultaneous gas chromatographic determination of carbofuran, metalaxyl, and simazine in soils.

A method for extraction, cleanup, and simultaneous gas chromatographic detection of carbofuran, metalaxyl, and simazine in soils has been developed. Pesticide residues were extracted from soil with acetone containing 10% 0.2M HCl-KCl buffer (pH 2.0), cleaned up with methylene chloride-carbonate buffer (pH 10.7) solvent partitioning and solid-phase extraction on disposable silica gel columns, and quantitated with gas chromatography using a Supelcowax 10 megabore capillary column and a nitrogen-selective detector. Method limits of detection were 0.02 microgram/g for the 3 pesticides in surface soils (0-30 cm depths) and 0.02, 0.02, and 0.005 microgram/g in soils below 30 cm (subsoils) for carbofuran, metalaxyl, and simazine, respectively. Recoveries for carbofuran, metalaxyl, and simazine were 92.6 +/- 5.5, 93.6 +/- 5.0, and 88.4 +/- 6.7%, respectively, when soil samples were spiked with pesticide concentrations ranging from 0.02 to 2.0 micrograms/g.