Effect of drying and composting biosolids on the movement of nitrate and phosphate through repacked soil columns under steady-state hydrological conditions

Sewage sludge composting: quality assessment for agricultural application

In order to use sewage sludge (SS) composts in agriculture, it is extremely important to estimate the quality of compost products. The aim of this study was to investigate the quality of composted SS as a fertilizer and soil amendment especially in semi-arid areas. To determine the quality and agronomic value of the SS compost products, analyses on pH, electrical conductivity, organic matter content, C/N ratio, phytotoxicity, microbial load, and heavy metal content of composted anaerobically digested SS, with different proportions (1:1, 1:2, and 1:3 v/v) of green and dry plant waste, as bulking agents, were performed. The 1:2 and 1:3 mixtures of SS and green/dry plant waste were the most beneficial for composting, with final composts attaining high organic matter degradation and exhibiting low amounts of heavy metals, a relatively high germination index, and significant reduction of pathogens, suggesting the agricultural relevance of composted SS and green/dry plant waste at 1:2 and 1:3 (v/v) proportions. pH and electrical conductivity were also within the permissible limits. With respect to international standards, it appears that composted SS and green/dry plant waste at 1:2 and 1:3 proportions pose no threat to soil or plant quality if used in agriculture or land restoration.

Escherichia coli removal in biochar-augmented biofilter: effect of infiltration rate, initial bacterial concentration, biochar particle size, and presence of compost

Bioretention systems and biofilters are used in low impact development to passively treat urban stormwater. However, these engineered natural systems are not efficient at removing fecal indicator bacteria, the contaminants responsible for a majority of surface water impairments. The present study investigates the efficacy of biochar-augmented model sand biofilters for Escherichia coli removal under a variety of stormwater bacterial concentrations and infiltration rates. Additionally, we test the role of biochar particle size and "presence of compost on model" biofilter performance. Our results show that E. coli removal in a biochar-augmented sand biofilter is ∼ 96% and is not greatly affected by increases in stormwater infiltration rates and influent bacterial concentrations, particularly within the ranges expected in field. Removal of fine (<125 μm) biochar particles from the biochar-sand biofilter decreased the removal capacity from 95% to 62%, indicating biochar size is important. Addition of compost to biochar-sand biofilters not only lowered E. coli removal capacity but also increased the mobilization of deposited bacteria during intermittent infiltration. This result is attributed to exhaustion of attachment sites on biochar by the dissolved organic carbon leached from compost. Overall, our study indicates that biochar has potential to remove bacteria from stormwater under a wide range of field conditions, but for biochar to be effective, the size should be small and biochar should be applied without compost. Although the results aid in the optimization of biofilter design, further studies are needed to examine biochar potential in the field over an entire rainy season.

Fate of triclosan and triclocarban in soil columns with and without biosolids surface application

The leaching and transformation behaviors of triclosan (TCS) and triclocarban (TCC) in soil columns (20 cm high, 4 cm in diameter) packed with an agricultural soil (Roxana very fine sandy loam) with and without biosolids surface application were investigated. The column leachates and soil samples were analyzed for TCS, TCC, and their transformation products. Significantly more TCS was transformed compared with TCC. Surface application of biosolids significantly retarded their transformation. Downward movement of TCS and TCC occurred within a 10-cm soil depth. Methyl-TCS was not detectable in the leachates but was detected in the top 5-cm soil layer, with more appearing in the biosolids-applied soil. At the end of the column study, carbanilide (CBA) was the only detectable TCC reductive dechlorination product in the soil. No TCC reductive dechlorination products were detectable in the leachates. Detection of 3,4-dichloroaniline (3,4-DCA) and 4-chloroaniline (4-CA) suggested the occurrence of TCC hydrolysis. Rapid leaching of 4-CA through the soil column was observed. The 3,4-DCA was detected throughout the entire 20-cm depth of the soil column but not in the leachates. The fact that only small percentages of the transformed TCS and TCC appeared, after a 101-d column study, in the forms of the products analyzed suggested that either the investigated transformation pathways were minor pathways or further rapid transformation of those products had occurred.

Comparison between pine bark and coconut husk sorption capacity of metals and nitrate when mixed with sewage sludge

Waste products such as biosolids and wood wastes have been frequently used in container production of plants. The use of biosolids in agriculture is a beneficial mean of recycling the by-products of waste-water treatment. However, care must be taken to avoid environmental or human health problems via run-off and leaching. The objective of this work is to compare the retention capacity of cadmium, lead, zinc and nitrate between pine bark (PB) and coconut fibre (F) when mixed with increasing amounts of composted sewage sludge (CSS) (0%, 15% and 30% (v/v)). Substrates were packed into leaching columns and irrigated with deionised water every 2 days. Leachates were collected during 1 month, and nitrate, Zn, Cd, Pb, EC and pH were monitored along the experiment. PB columns leached lower amount of nitrate than the coconut fibre ones. The same trend was observed for Zn, Cd and Pb. It could be said, that in order to minimize the environmental risks of using sewage sludges our results indicate that it is preferred to mix the sludge with pine bark instead than with coconut husk.