Tomato Yield and Quality and Emitter Clogging as Affected by Chlorination Schemes of Drip Irrigation Systems Applying Sewage Effluent

Chlorination has been recognized as an efficient and economically favorable method for treating clogging in drip emitters caused by biological growth during sewage application. Further important criteria for determining an optimal chlorination scheme are the different responses of crops to the chloride added into the soil through chlorination. During two seasons in 2008 and 2009, field experiments were conducted in a solar-heated greenhouse with drip irrigation systems applying secondary sewage effluent to tomato plants to investigate the influences of chlorine injection intervals and levels on plant growth, yield, fruit quality, and emitter clogging. Injection intervals ranging from 2 to 8 wk and injection concentrations ranging 2-50 mg L-1 of free chlorine residual at the end of the laterals were used. For the 2008 experiments, the yield from the treatments of sewage application with chlorination was 7.5% lower than the yield from the treatment of sewage application without chlorination, while the yields for the treatments with and without chlorination were similar for the 2009 experiments. The statistical tests indicated that neither the chlorine injection intervals and concentrations nor the interactions between the two significantly influenced plant height, leaf area, or tomato yield for both years. The qualities of the fruit in response to chlorination were parameter-dependent. Chlorination did not significantly influence the quality of ascorbic acid, soluble sugar, or soluble acids, but the interaction between the chlorine injection interval and the chlorine concentration significantly influenced the levels of soluble solids. It was also confirmed that chlorination was an effective method for reducing biological clogging. These results suggested that chlorination is safe for a crop that has a moderate sensitivity to chlorine, like tomato, and can maintain a high level of performance in drip irrigation systems applying sewage effluent.

Effects of Chlorination on Soil Chemical Properties and Nitrogen Uptake for Tomato Drip Irrigated with Secondary Sewage Effluent

Chlorination is usually an economical method for treating clogging in drip emitters during sewage application. Appropriate assessment of the responses of soil and crop is essential for determining an optimal chlorination scheme. During 2008 to 2009, field experiments were conducted in a solar-heated greenhouse for tomato drip irrigated with secondary sewage effluent, to investigate the influences of chlorine injection intervals and levels on soil chemical properties and nitrogen uptake. Injection intervals ranging from two to eight weeks and injection concentrations ranging from 2 to 50 mg L-1 were used. A salinity factor and a nutrient factor were extracted from the pool of the nine soil chemical constituents using factor analysis method. The results demonstrated that chlorination practices increased the residual Cl in the soil, resulting in an increased salinity factor, especially for the frequent chlorination at a high injection concentration. Chlorination weakened the accumulation of nutrients factor in the upper soil layer. Nitrogen uptake of the tomato plants also was inhibited by the increased salinity in the upper soil layer caused by high chlorination levels. In order to reduce the unfavorable effect on soil chemical properties and nitrogen uptake, chlorination scheme with concentrations of lower than 20 mg L-1 was recommended.

Microalgae as Bioabsorbents for Treating Mixture of Electroplating and Sewage Effluent

The effectiveness of copper and nickel uptake by microalgae grown in the mixture of electroplating effluent and sewage was studied. The results showed that a high percentage of copper removal (68.1%-88.2%) was achieved by Chlorellapyrenoidosa (strain No. 26) reared in the mixture of 90% electroplating effluent and 10% raw sewage during the first 3 days despite the fact that cell growth was inhibited. Similar results were also obtained by using Chlorella HKBC-C3, another species collected from one of the heavy metal polluted sites in Hong Kong, isolated and cultured in the Biology Department. There was no significant difference (P>0.05) in the removal of copper and nickel from the effluent between these 2 algal species. However, it was noted that removal of nickel from the mixture by the two species were comparatively lower (<20%) than the removal of copper (>68%).

Modeling Cadmium Transport in Neutral and Alkaline Soil Columns at Various Depths

Human health has been potentially threatened by cadmium (Cd) contained in sewage irrigation water.Previous studies of Cd transport in soils were mainly conducted using small soil cores with pH values less than 6.The objectives of this study were to determine the parameters of the convection-dispersion equation (CDE) for Cd transport in relatively larger columns with neutral and alkaline soils,and to investigate the parameters' variability with depth.The soil columns were 50 cm in length and 12.5 cm in diameter.Ceramic suction lysimeters were buried at depths of 2.5,7.5,17.5,27.5,and 37.5 cm to abstract soil solution.Cd concentration in the soil solution samples were subsequently analyzed to obtain breakthrough curves (BTCs).Equilibrium and nonequilibrium models in CXTFIT program were used to estimate parameters of the CDE.The results suggested that both equilibrium and non-equilibrium models performed well in modeling Cd transport.The hydrodynamic dispersion coefficient (D) ranged from 0.18 to 10.70 cm 2 h 1,showing large differences among different depths.The retardation factor (R d) ranged from 25.4 to 54.7 and the standard deviation of R d value was lower than 30% of the mean value.Precipitation coefficient (R p) decreased consistently with increasing depth,varying from 1.000 × 10 10 to 0.661 h 1.Sensitivity tests showed that D was less sensitive than R d.These results would be helpful in understanding the transport and retention of Cd in non-acidic soils.

Local Persistence of Large Benthic Foraminifera(LBF)under Increasing Urban Development:A Case Study from Zanzibar(Unguja),East Africa

Coastal marine management is vital for socio-ecological sustainability of developing,tropical ecosystems,which calls for diverse tools to monitor and assess water quality.The carbonatedominated habitats off Zanzibar were chosen for study due to potential water quality degradation in a rapidly developing tourist destination heavily reliant on its coral reefs.These reefs are largely unmonitored and subject to local and global stressors.A widely used method for assessing reef health,as an early detection method of ecological changes,is the application of large benthic foraminiferal bioindicators,i.e.,the Fo RAM Index.We expected to find poor water quality conditions in the unmanaged reefs supported by stress-toelerant(opportunistic)foraminiferal assemblages.The dissolved inorganic nitrogen and phosphate values derived from untreated sewage effluent from Stone Town were highly variable(ranging 0.05–3.77 and 0.05–1.45μM,respectively),moderate,and occasionally approached or exceeded critical threshold values for oligotrophic ecosystems.The analysis of total assemblages indicated an abundance of symbiont-bearing large benthic foraminifera,dominated by prolific Amphistegina species,comparatively low-moderate diversity,high FI values(7.6 on average),and high coral cover.A water quality gradient was reflected by subtle assemblage differences,suggesting that LBF can provide early warning signals of benthic changes,indicating the importance of long-term monitoring programs in vulnerable,rapidly developing coastal ecosystems exposed to increasing pressures.

Neural stem cell-based in vitro bioassay for the assessment of neurotoxic potential of water samples

Intensive agriculture activities,industrialization and growing numbers of wastewater treatment plants along river banks collectively contribute to the elevated levels of neurotoxic pollutants in natural water reservoirs across Europe.We established an in vitro bioassay based upon neural stem cells isolated from the subventricular zone of the postnatal mouse to evaluate the neurotoxic potential of raw wastewater,treated sewage effluent,groundwater and drinking water.The toxic potential of water samples was evaluated employing viability,proliferation,differentiation and migration assays.We found that raw wastewater could reduce the viability and proliferation of neural stem cells,and decreased the neuronal and astrocyte differentiation,neuronal neurite growth,astrocyte growth and cell migration.Treated sewage water also showed inhibitory effects on cell proliferation and migration.Our results indicated that relatively high concentrations of nitrogenous substances,pesticides,mercuric compounds,bisphenol-A,and phthalates,along with some other pollutants in raw wastewater and treated sewage water,might be the reason for the neuroinhibitory effects of these water samples.Our model successfully predicted the neurotoxicity of water samples collected from different sources and also revealed that the incomplete removal of contaminants from wastewater can be problematic for the developing nervous system.The presented data also provides strong evidence that more effective treatments should be used to minimize the contamination of water before release into major water bodies which may be considered as water reservoirs for human usage in the future.