Unveiling the role of sediments in phosphorus removal in pilot-scale constructed wetlands for swine wastewater treatment.

The accumulation rate, fractions, and sorption capacity of phosphorus in sediments determine the removal efficiency and service life of constructed wetlands (CWs). Nine pilot-scale three-stage surface flow CWs were constructed to treat three loading rates of lagoon-pretreated swine wastewater, and surface sediment samples at initial and one-year treatment were collected to analyze the phosphorus fractions and sorption capacity. After one-year treatment, concentration of total phosphorus (TP) in sediments increased for high loading rates of wastewater, but remained stable for low loading rates. The annual accumulation rate of TP in sediments (Ma) was -43-445 mg kg-1 yr-1 at surface loading rate (SLR) of 36-355 g P m-2 yr-1. Their association could be described well using a sigmoid model, i.e., Ma = -23 + 538/(1 + exp.(-(SLR-262)/48)) (R2adj = 0.897, RMSE = 40.8, p < 0.01), indicating that the phosphorus accumulation rates in sediments were loading rate-dependent. The sum of inorganic phosphorus fractions contributed to 80-100% of the TP concentration, and accumulation of aluminum-bound phosphorus (AlP) and iron-bound phosphorus (FeP) was responsible for variability of TP concentration in sediments. Phosphorus sorption capacity of CW1 sediments increased by 1.3-1.8 times, attributed to increased pH, and concentrations of ammonium oxalate-extractable aluminum and iron in sediments due to the wastewater input. Selecting iron and aluminum-rich materials preferentially as substrates and regulating the ratio of metal ions to phosphorus in wastewater should be alternative enhancement strategies of CWs for phosphorus removal.

[Decomposition of Myriophyllum aquaticum and the Associated Release of Nitrogen and Phosphorus].

Decomposition of wetland plants could release pollutants, which may affect the removal efficiency and effluent quality of constructed wetlands. The experimental decomposition test of Myriophyllum aquaticum was carried out for 60 d using nylon bags, and release characteristics of nitrogen and phosphorus during the decomposition process were studied. The results showed that the decomposition rate of M. aquaticum was fastest during the first 0-4 d, with a weight loss of 30%, while the degradation rate slowed gradually during the period 4-60 d, with weight loss of 31%. The fitting first-order kinetic decomposition rate constant was 0.0142 d-1, and the calculated time to degrade 50% of dry matter was 48.8 d. The water pH decreased rapidly from 7.60 to 5.63 during 0-4 d, stabilized during 4-32 d, and finally increased to 7.03 (which was close to the control sample without M. aquaticum). The dissolved oxygen concentration decreased rapidly from 6.30 mg·L-1 to 0.61 mg·L-1 during 0-4 d, and remained in an anaerobic state. The total nitrogen concentration in the water increased rapidly to 12.7 mg·L-1 within 2 h, gradually decreased to 5.80 mg·L-1 during 2 h-32 d, and then finally increased slightly. The phosphorus concentration increased rapidly to 18.4 mg·L-1 at the beginning of the experiment, and then gradually stabilized. The main forms of nitrogen and phosphorus released by M. aquaticum were organic nitrogen (accounting for 65.7%-94.7% of total nitrogen) and inorganic phosphorus (accounting for 61%-89% of total phosphorus), respectively. The total nitrogen content of M. aquaticum increased from 24.3 mg·g-1 to 60.5 mg·g-1 with increasing degradation time; the total phosphorus decreased initially from 6.09 mg·g-1 to 2.94 mg·g-1 and then remained constant. These trends may have been related to the fixation of nitrogen by attached microorganisms. Therefore, suitable harvesting and management strategies should be adopted for wetland plants to reduce secondary pollution.

Effect of controlled-release fertilizer on N2O emissions and tea yield from a tea field in subtropical central China.

Tea (Camellia sinensis L.), a perennial leaf-harvested crop, favors warm/humid climate and acidic/well-drained soils, and demands high nitrogen (N) fertilizer inputs which lead to significant emissions of N2O. Potential mitigation options should be adopted to improve N use efficiency (NUE) and reduce environmental pollution in tea field system. A 3-year field experiment was carried out in a tea field in southern China from January 2014 to December 2016 to investigate the effect of controlled-release fertilizer (CRF) application on N2O emissions in tea field system. Three practices, namely conventional treatment (CON, 105 kg N-oilcake ha-1 year-1 + 345 kg N-urea ha-1 year-1), treatment with a half amount of the N fertilizer (CRF50%, 105 kg N-oilcake ha-1 year-1 + 120 kg N CRF ha-1 year-1) and full amount of N fertilizer (CRF100%, 105 kg N-oilcake ha-1 year-1 + 345 kg N CRF ha-1 year-1) were used. Compared with the CON, our results showed that CRF50% reduced the N2O emissions by 26.2% (p > 0.05) and increased the tea yield by 31.3% (p > 0.05), while CRF100% significantly increased the N2O emissions by 96.7% (p < 0.05) and decreased the tea yield by 6.77% (p > 0.05). Overall, yield-scaled N2O emissions of tea were reduced by 44.5% (p > 0.05) under CRF50% and significantly increased by 100% (p < 0.05) under CRF100%, compared with CON. Based on the gross margin analysis, CRF50% obtained the highest net economic profit. Our findings suggest that reducing N input of CRF (CRF50%) is necessary and feasible for adoption in the current tea plantation system.

[Physiological Characteristics and Nitrogen and Phosphorus Uptake of Myriophyllum aquaticum Under High Ammonium Conditions].

Ammonium nitrogen (NH4+-N) at high concentrations is toxic to plants. In order to explore the NH4+-N tolerance of Myriophyllum aquaticum (M. aquaticum) and its ability of nitrogen (N) and phosphorus (P) uptake, this study used a nutrient solution with three NH4+-N levels (70, 210, 420 mg·L-1) to incubate M. aquaticum for 21 d. The characteristics of plant physiology and N and P uptake of M. aquaticum were measured. At NH4+-N of 70 mg·L-1, M. aquaticum grew healthily, and shoot height and biomass linearly increased with the increase incubation time. Relative shoot height and biomass of M. aquaticum were 40.56 cm and 17.82 g·hole-1 on day 21, respectively. Compared to the control with 70 mg·L-1 ammonium, malondialdehyde (MDA) content of M. aquaticum was significantly increased; chlorophyll and soluble sugar contents were also high at NH4+-N of 210 mg·L-1. M. aquaticum suffered from the NH4+-N stress. However, the stress of 210 mg·L-1 NH4+-N did not affect its normal growth and there was no significant difference in the relative growth rate of the shoot height and biomass compared with the control. At NH4+-N of 420 mg·L-1, MDA contents of M. aquaticum doubled and the shoot height and biomass growth rate were only 27.4% and 17.9% of those for 70 mg·L-1 NH4+-N, indicating that M. aquaticum was subjected to serious stress that caused unhealthy growth or even death. At three NH4+-N levels, the ranges of N and P content of M. aquaticum were 30.7-53.4 mg·g-1 and 3.8-7.7 mg·g-1, respectively, which indicated that M. aquaticum had a high uptake capacity of N and P. M. aquaticum is an ideal wetland plant that has a good application prospect for constructed wetlands in biological treatment of high-ammonia wastewater.

[Interception Effect of Vegetated Drainage Ditch on Nitrogen and Phosphorus from Drainage Ditches].

In order to effectively intercept and remove nitrogen (N) and phosphorus (P) from agricultural water, Canna glauca, Sparganium stoloniferum, Juncus effusus, Hydrocotyle vulgaris, and Myriophyllum elatinoides were planted in an agricultural drainage ditch. The temporal and spatial variations of the dissolved N and P concentrations were monitored during the whole experimental period. In addition, the contents of N and P in sediments and plants were compared among different plant plots. The results showed the effluent TN and TP concentrations in the vegetated drainage ditch were lower than the surface water environmental quality standards for class IV and class II . The average removal rates of TN and TP in water were 64.3% and 69.7%, respectively. The average sediment interceptions in 2010 and 2011 reached 40,400 kg, containing 52.4 kg of N and 21.4 kg of P. The amounts of sediment N and P in five plant plots exhibited the descending order: Canna glauca > Hydrocotyle vulgaris > Sparganium stoloniferum > Myriophyllum elatinoides > Juncus effuses. The accumulated N and P amounts assimilated by five kinds of aquatic plants reached 7.9 kg · a⁻¹ and 1.4 kg · a⁻¹, respectively. Compared with other plants, Canna glauca and Myriophyllu elatinoides had the highest ratios of above-ground and below-ground tissues, and the strongest absorption capacity of N and P was also observed in these two plants. Therefore, the vegetated drainage ditch has good interception effect on N and P pollutants. Furthermore, Canna glauca and Myriophyllum elatinoides can be considered as the optimal plants for N and P uptake.

Mitigating nitrous oxide emissions from tea field soil using bioaugmentation with a Trichoderma viride biofertilizer.

Land-use conversion from woodlands to tea fields in subtropical areas of central China leads to increased nitrous oxide (N2O) emissions, partly due to increased nitrogen fertilizer use. A field investigation of N2O using a static closed chamber-gas chromatography revealed that the average N2O fluxes in tea fields with 225 kg N ha(-1) yr(-1) fertilizer application were 9.4 ± 6.2 times higher than those of woodlands. Accordingly, it is urgent to develop practices for mitigating N2O emissions from tea fields. By liquid-state fermentation of sweet potato starch wastewater and solid-state fermentation of paddy straw with application of Trichoderma viride, we provided the tea plantation with biofertilizer containing 2.4 t C ha(-1) and 58.7 kg N ha(-1). Compared to use of synthetic N fertilizer, use of biofertilizer at 225 kg N ha(-1) yr(-1) significantly reduced N2O emissions by 33.3%-71.8% and increased the tea yield by 16.2%-62.2%. Therefore, the process of bioconversion/bioaugmentation tested in this study was found to be a cost-effective and feasible approach to reducing N2O emissions and can be considered the best management practice for tea fields.

Bioconversion of wastewater from sweet potato starch production to Paenibacillus polymyxa biofertilizer for tea plants.

Wastewater from the sweet potato starch industry is a large source of nutrient-rich substrates. We assessed whether this wastewater could be used to produce Paenibacillus polymyxa biofertilizer for foliar application to tea trees. Using the central composite design methods we experientially determined that the optimal culture conditions for P. polymyxa were pH, 6.5; temperature, 29.0 °C; and incubation time, 16 h. Under these conditions, a maximum biomass of 9.7 × 10(9) cfu/mL was achieved. We then conducted a yearlong field investigation to determine the effect of P. polymyxa biofertilizer on the growth of tea plants (Camellia sinensis). Tea yield, quantity of water extract, and tea polyphenol levels were significantly higher after foliar application of the biofertilizer compared to that in the controls by an average of 16.7%, 6.3%, and 10.4%, respectively. This approach appears to be technically feasible for organic tea production, and is an environmentally friendly way to utilize wastewater.

[Study on phosphorus adsorption characteristic of sediments in an ecological ditch].

Sediments properties and phosphorus (P) adsorption capacities were compared among the samples of 0-5 cm and 5-15 cm layers from the ecological ditch vegetated with Cenetlla asiatica, Sparganium stoloniferum and a natural agricultural ditch with weeds. The results showed the 0-5 cm sediment vegetated with Cenetlla asiatica had higher concentrations of oxalate extracted Fe, Al and P than those vegetated with Sparganium stoloniferum or weeds. The parameters calculated from the Freudlich and Langmiur isotherms showed the equilibrium phosphate concentration (EPC0) ranged from 0.009 to 0.031 mg x L(-1). Cenetlla asiatica in the 0-5 cm layer had the maximum values of 352.2 L x kg(-1) and 562.7 mg x kg(-1) for Freundlich adsorption constant (K(f)) and Langmuir sorption maximum (S(max)), respectively, which proved it had the highest P adsorption capacity. The regression analysis showed P sorption parameters had significant relationship to oxalate-extracted Fe, clay content and DPS (P < 0.05). It was thus clear that aquatic plants influenced sediment properties and P adsorption capacity, and the practice of growing proper plants in ecological ditch could reduce the risk of P loss in non-point source pollution.

[Effects of mulching and intercropping on temporal-spatial variation of soil temperature in tea plantation in subtropical hilly region].

The study of four years straw mulching and white clover intercropping in a tea plantation in subtropical hilly region showed that the soil temperature in the plantation presented a distinct dynamic temporal-spatial variation and hysteresis, which was greatly accorded with the fittest temperature of tea growth. Straw mulching and white clover intercropping altered the nature of soil thermal exchanging layer (soil surface), decreased daily temperature difference, enhanced the temperature stability in the same soil layer, and had duplex effects of lowering temperature when it went up and increasing and keeping temperature when it went down. The effectiveness was in the order of white clover intercropping > straw mulching > control, 13:00 > 19:00 >7:00,and lowering temperature > increasing and keeping temperature, and decreased with soil depth. Straw mulching and white clover intercropping adjusted the switching point of the temporal-spatial variation of soil temperature, and evidently decreased the emergence of harmful high temperature. During the period of continual high temperature, these measures markedly lowered soil temperature, and effectively shortened the duration of this period.