Harnessing fertilizer potential of human urine in a mesocosm system: a novel test case for linking the loop between sanitation and aquaculture

Human urine (HU) is a biogenic fertilizer which has raised immense interest owing to its capacity of combining sanitation and nutrient recovery. In search of an alternative organic fertilizer for fish culture, the nutrient potential of HU was evaluated. Fries of Indian carps and larvae of freshwater prawn were reared for 120 days under six conditions: (a) aerated and (b) non-aerated fresh HU (0.01%), (c) cattle manure (CM; 1.8 kg tank⁻¹), mixed treatment with CM and HU under (d) iso-phosphorus and (e) iso-nitrogenous condition and (f) control. Monitoring of water quality and biological parameters revealed that total fish yield was the highest in CM (621.5 g tank⁻¹) followed by mixed treatments under iso-nitrogenous (428 g tank⁻¹) and iso-phosphorus (333 g tank⁻¹) conditions, aerated HU (321 g tank⁻¹) and HU (319 g tank⁻¹). The gross primary productivity (GPP) in HU was satisfactory (601.8 mg C m⁻² h⁻¹) and superior to all but CM treatment. The abundance of heterotrophic bacteria (HB) was highest in CM and lowest in HU. Both GPP and HB population were correlated positively with fish yield per tank. Although pH in all treatments remained high (pH 8.4–8.9), no ammonia toxicity was observed. No E. coli infestation in any fish muscle was encountered. The concentrations of cadmium and lead in fish muscle were within respective safe level. The study established that high fertilizer potential of HU could be exploited as an alternative organic fertilizer or as a candidate to be blended with cattle manure.

     

Correction to: Influence of physico-chemical properties of soil clay fractions on the retention of dissolved organic carbon

Environmental Geochemistry and Health - Unfortunately, in the original publication of the article, Prof. Yong Sik Ok’s affiliation was incorrectly published. The author’s affiliation is...     

Effect on herbicide adsorption of organic forestry waste products used for soil remediation

Organic soil amendments can be useful for improving degraded soil, but this increase in organic matter (OM) may influence adsorption of herbicides subsequently applied to the treated soil, even though the particle size of amendments and their nature differ from typical soil OM. In this study, a batch equilibrium method was used to measure adsorption of five herbicides following application to two organic media, wood pulp and sawdust, comparing these with two cropping soils. Herbicide adsorption, quantified by distribution coefficients (k_d), was much higher in the two organic media than in the cropping soils. The increases in adsorption were strongly correlated to the percentage of organic carbon. When the k_d was normalized to adsorption coefficients corrected for OM content (k_oc), variation in results between the media was greatly reduced, indicating that OM is an important factor influencing adsorption in these media. The results of this study suggest that herbicides will be less effective when applied to soils in which sawdust and wood pulp have been added. Using organic amendments to remediate soil will increase adsorption of pesticides, reducing their bio-availability and efficacy, but also reducing their tendency to leach into root zones of deep-rooted crops and into groundwater.     

Influence of physico-chemical properties of soil clay fractions on the retention of dissolved organic carbon

This study investigated the effects of surface functional groups, cation exchange capacity (CEC), surface charge, sesquioxides and specific surface area (SSA) of three soil clay fractions (SCFs) (kaolinite–illite, smectite and allophane) on the retention of dissolved organic carbon (DOC) in soils. Physico-chemical properties of the SCFs before and after removing native carbon and/or sesquioxides were characterised, and the DOC adsorption–desorption tests were conducted by a batch method. Native organic carbon (OC)/sesquioxide removal treatments led to a small change in the CEC values of kaolinite–illite, but significant changes in those of smectite and allophane. The net negative surface charge increased in all samples with an increase in pH indicating their variable charge characteristics. The removal of native OC resulted in a slight increase in the net positive charge on soil clay surfaces, while sesquioxide removal increased the negative charge. Changes in the functional groups on the SCF surfaces contributed to the changes in CEC and zeta potential values. There was a strong relationship (R ² = 0.93, p < 0.05) between the Langmuir maximum DOC adsorption capacity (Q _max) and SSA. The Q _max value also showed a moderately strong relationship (R ² = 0.55, p < 0.05) with zeta potential (at pH 7). Q _max was only poorly correlated with CEC and native OC content. Therefore, along with SSA, the surface charge and functional groups of SCFs played the key role in determining the adsorption affinity and hence retention of DOC in soils.     

Concomitant rock phosphate dissolution and lead immobilization by phosphate solubilizing bacteria (Enterobacter sp.)

This paper examines the potential value of phosphate solubilizing bacteria (Enterobacter cloacae) in the dissolution of rock phosphate (RP) and subsequent immobilization of lead (Pb) in both bacterial growth medium and soils. Enterobacter sp. showed resistance to Pb and the bacterium solubilized 17.5% of RP in the growth medium. Enterobacter sp. did not enhance Pb immobilization in solution because of acidification of bacterial medium, thereby inhibiting the formation of P-induced Pb precipitation. However, in the case of soil, Enterobacter sp. increased Pb immobilization by 6.98, 25.6 and 32.0% with the RP level of 200, 800 and 1600 mg P/kg, respectively. The immobilization of Pb in Pb-spiked soils was attributed to pyromorphite formation as indicated by XRD analysis. Inoculation of phosphate solubilizing bacteria with RP in soil can be used as an alternative technique to soluble P compounds which can cause eutrophication of surface water.