Effectiveness of cyclic irrigation in reducing suspended solids load from a paddy-field district

The reduction of suspended solids, nutrients, and organic matter loads in drainage water from paddy fields is an important issue for water quality management in closed water areas in Japan. We evaluated the ability of cyclic irrigation to reduce the suspended solids load from paddy fields. In 2006 and 2007, we investigated water and mass balances during the irrigation period in a low-lying paddy-field district neighboring Lake Biwa, which is the largest lake in Japan. We confirmed that cyclic irrigation reduced effluent loads during the puddling season. With cyclic irrigation, 118 kg ha−1 of suspended solids was returned to the paddy fields in 2006 and 199 kg ha−1 in 2007. The effect of cyclic irrigation on the net suspended solids load can be represented by three ratios: the concentration ratio, which represents the ratio of the suspended solids concentration in drainage water to that in lake water; the cyclic irrigation ratio, which represents the ratio of the volume of reused water to that of irrigation water in cyclic irrigation; and the surplus irrigation water ratio, which represents the ratio of the volume of surplus irrigation water to that of irrigation water. The cyclic irrigation ratio and the surplus irrigation water ratio interact to determine the effect of cyclic irrigation on the net suspended solids load. Simultaneously increasing the cyclic irrigation ratio and decreasing the surplus irrigation water ratio will maximize the purification effect on drainage water from paddy fields

Effects of cyclic irrigation on water and nitrogen mass balances in a paddy field

Cyclic irrigation is considered an effective water management practice for reducing pollutant loads from a paddy-field district. The objective of this study was to clarify the effects of cyclic irrigation on mass balance in paddy plots. At the study site, cyclic irrigation with a high cyclic irrigation ratio (% reused water in irrigation water) was conducted from late April to late June. We found a complementary relationship between the volume of irrigation water and rainfall, which together totaled about 1400–1600 mm during the irrigation period each year. We concluded that a cyclic irrigation system that enables the paddy-field district to use a high cyclic irrigation ratio may lead to more efficient use of rainfall for crop irrigation. Nitrogen concentrations in both irrigation water and ponded water tended to be higher during the cyclic irrigation period than during the lake water irrigation period. Nitrogen input from irrigated water accounted for about 8–16% of the total input of nitrogen. It is suggested that fertilizer application of nitrogen can be reduced by its return through cyclic irrigation

Reducing the phosphorus effluent load from a paddy-field district through cyclic irrigation

Phosphorus (P) effluent load discharged from paddy fields has a substantial impact on water quality in downstream areas. We evaluated the effectiveness of cyclic irrigation, in which drainage water is reused for irrigation purposes, in reducing the P load from a paddy-field district neighboring Lake Biwa, Japan. We measured temporal variations in the P concentration in drainage water and estimated the P mass balance for the study district for three consecutive years (2007–2009). A simple model was developed to characterize the hydrological structure and effects of cyclic irrigation using three parameters: the ratio of the P concentration in drainage water to that in irrigation water, the degree to which drainage water is reused, and the ratio of surplus irrigation water to the total amount of irrigation water. The total annual exports of P were 2.62–3.13 kg ha^{–1}. Phosphorus exports during the cyclic irrigation periods (April–June) were 0.27–0.63 kg ha^{–1} (period average rate = 3.7–8.8 g ha^{–1} d^{–1}), lower than those during the lake water irrigation periods (July–August) of 0.82–1.66 kg ha^{–1} (8.9–18.0 g ha^{–1} d^{–1}). Phosphorus export was lowest during the cyclic irrigation period, consistent with the small amounts of discharged drainage water. Our results suggest that cyclic irrigation is an effective district-scale method for reducing effluent P loads. Reuse of drainage water and efficient use of irrigation water are important in reducing the P load from the district

Review on stabilization/solidification methods and mechanism of heavy metals based on OPC-based binders

Stabilization/solidification (S/S) with ordinary portland cement (OPC)-based binders is a suitable method to remediate heavy metal (HM)-contaminated soil and reuse resources of industrial wastes. In industrial wastes, alkaline wastes such as red mud (RM), soda residue (SR), pulverized fly ash (PFA), and alkalinity granulated blast furnace slag (GGBS) can immobilize HM ions (Pb²⁺, Zn²⁺, Cd²⁺, Cr³⁺, and Cu²⁺) by precipitation. However, some HM ions (such as AsO₄³⁻) would redissolve within the strong alkali environment. In this case, PFA, GGBS, metakaolin (MK), and incinerated sewage sludge ash (ISSA) which have low pH, can be used to immobilize HM ions or added to the OPC-based binders to adjust the pH in the soil products. Moreover, the calcium silicate hydrate (CSH), calcium aluminum silicate hydrate (CASH), ettringite (AFt), and calcium monosulfoalumiante hydrates (AFm) generated during the pozzolanic reaction can also immobilize HM ions by adsorption on the surface, ion exchange, and encapsulation. SR and GGBS can be used to immobilize the HMs (such as CrO₄²⁻ and AsO₄³⁻), which are mainly affected by AFt and AFm. For those not affected by AFt and AFm but related to immobilization by precipitating (such as Mn²⁺), other wastes except SR and GGBS are suitable for treating contaminated soil. Nevertheless, the formation of AFt is also instrumental for soil product strength. There are several factors affecting soil product strength. In the future, the influence of different hydration products on the S/S effects, competitive adsorption of HM ions, effects on long-term HM stabilization, and novel materials are worth being explored by researchers

A novel reactor combining anammox and Fenton-like reactions for the simultaneous removal of organic carbon and nitrogen at different organic carbon to nitrogen ratios

Highlights Established FenTaMox process on Fe–Mn-sepiolite at neutral pH. FenTaMox simultaneously removed N and COD under high salinity and anaerobic condition. Enabled simultaneous removal of N and COD even at high COD/N ratio of 4. Fast COD removal by Fenton-like reaction prevented the predominance of denitrification. Marine anammox bacteria maintained the activity at H2O2 concentration up to 60 mg L−1 Abstract A Fenton-like reaction and anaerobic ammonium oxidation (anammox) were combined to construct a novel process named FenTaMox for removing nitrogen (N) and organic carbon (measured as chemical oxidation demand (COD)). Two columns were packed with iron-manganese-sepiolite, a catalyst that uses hydrogen peroxide (H2O2) to catalyze Fenton-like reactions, and inoculated with marine anammox bacteria. During the start-up, marine anammox medium was fed into both columns to acclimate the marine anammox bacteria to iron-manganese-sepiolite. Batch experiments revealed that the marine anammox bacteria were not affected by 60 mgL−1 of H2O2. Next, medium containing glucose and H2O2 was fed into one column as the FenTaMox treatment, while medium containing glucose but no H2O2 was fed into the other column as the control. At a COD/N of 4, FenTaMox exhibited higher removal efficiencies of N and COD compared with that of the control, suggesting the application of FenTaMox for organic carbon- and N- removal

Mitigation of heating of an urban building rooftop during hot summer by a hydroponic rice system

The use of green roofs is an important method for mitigating heating of urban rooftop environments. Our study aimed to demonstrate the mitigation of thermal effects on a hot rooftop during summer by a hydroponic system in which rice was grown. The system was installed on the top of a commercial building in the large city of Osaka, Japan; the roof was divided into two areas, one bare, the other covered by the hydroponic system. In both areas, we measured thermal factors, such as air temperature, rooftop surface temperature, and conductive heat flux; from the data we calculated three thermal mitigation indices. We also propose normalized types of mitigation indices. Mitigation effects on the thermal environment by the hydroponic system could be well estimated from ambient air temperature and solar radiation; the effects were better explained by solar radiation than by ambient air temperature. The results indicate that during the hot season, the system's mitigation effects on the thermal environment can be predicted from solar radiation level, and the normalized mitigation index is an appropriate index for estimating the cooling effect. Our results suggest that the hydroponic system might affect the energy flow in two ways: the proportions of sensible heat flux and latent heat flux are mainly affected by evaporative cooling and the portion of conductive heat flux is mainly affected by radiation shielding