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Bioretention systems have been implemented as stormwater best management practices (BMPs) worldwide to treat non-point sources pollution. Due to insufficient research, the design guidelines for bioretention systems in tropical countries are modeled after those of temperate countries. However, climatic factors and stormwater runoff characteristics are the two key factors affecting the capacity of bioretention system. This paper reviews and compares the stormwater runoff characteristics, bioretention components, pollutant removal requirements, and applications of bioretention systems in temperate and tropical countries. Suggestions are given for bioretention components in the tropics, including elimination of mulch layer and submerged zone. More research is required to identify suitable additives for filter media, study tropical shrubs application while avoiding using grass and sedges, explore function of soil faunas, and adopt final discharged pollutants concentration (mg/L) on top of percentage removal (%) in bioretention design guidelines.

Conventional activated-sludge (AS) technologies are deficient for nutrient removal because they require specific floc characteristics. Therefore, the encapsulated AS with polyvinyl alcohol (PVA) will favor floc's formation that removes nutrients. The applied method was based on monitoring the removal of organic matter and nutrients (NH 4 + , NO 3 - , NO 2 - , PO 4 3- ) from synthetic domestic wastewater using laboratory-scale AS. The experimental reactors were operated at 8 h as optimized Hydraulic Retention Time (HRT). The sludge characteristics evaluation was carried out through the Sludge Volumetric Index (SVI), Food/Microorganism ratio (F/M), and Mixed Liquor Volatile Suspended Solids (MLVSS). Other specific floc characteristics, such as zeta potential and effective diameter were also evaluated. The results showed that the encapsulated AS with PVA favors nitrogen and phosphorous removal up to 35% but it did not improve organic matter removal. In addition, encapsulated AS with PVA has the characteristics of filamentous sludge (F/M: 0.7 g COD g -1 MLVSS d -1 ) with good settleability conditions (SVI: 43 mL g -1 MLSVS h -1 ) and low zeta potential (ZP: -0.9 mV), which favors its separation from the liquid phase. In conclusion, the encapsulation of AS with PVA improves nutrient removal by improving floc characteristics.

Bioretention cells have become one of the most popular devices in urban stormwater runoff management for their high efficiency in reducing runoff volume and pollution loads. However, bioretention cells are unstable in nutrient pollutant removal, as is verified by many cases, especially at low temperatures. Dissolved organic matters (DOMs) plays an important role in denitrification, but the three-dimensional fluorescence characteristics of stormwater runoff in bioretention field cells are poorly understood, so to improve the performance of bioretention cells in nutrient pollutants control, the authors determined that it was necessary to clarify the characteristics of three-dimensional fluorescence of stormwater runoff from bioretention cells and explain their relationship to water quality. To be applicable to urban landuse in mountainous cities, two field lined bioretention cells were constructed, and, from March to April in 2017, while temperatures were still low, water quality and three-dimensional fluorescence of stormwater runoff were analyzed during low rainfall intensity precipitation events. Analysis results showed that the effluent pollutant concentrations had low fluctuation after purification by the bioretention cells, and both cells showed relatively stable removal rates for NH 4 + -N and total phosphorus (TP; i. e., 78.38%-95.03% and 72.04%-76.04%, respectively). Analysis of fluorescence spectra showed that the DOMs in the runoff from the two cells was mostly made up of protein and humic substances, mainly of biological origin or aquatic bacterial metabolites. Both cells performed well in the removal of protein at I, protein at Ⅱ and fulvic acid (i. e., the removal rates could reach 57.33%-61.30%, 29.82%-31.28%, and 35.55%-43.16% respectively). Correlation analyses between water quality and DOM showed that total Nitrogen (TN), TP and total organic carbon (TOC) were positively correlated with the protein content in runoff from the biorentention cells, while NO 3 - -N and NH 4 + -N were negatively correlated with protein content. Meanwhile, TN was negatively correlated with DOMs in regions Ⅳ and Ⅴ of the cells.

A new integrated water remediation technology, including a floating bed, a buffer zone of floating plants, enclosed 'water hyacinth' purification, economic aquatic plants and near-shore aquatic plant purification, was used in Dishui Lake to improve its water quality. A channel of 1,000 m length and 30 m width was selected to implement pilot-scale experiments both in the static period and the continuous water diversion period. The results showed that the new integrated water remediation technology exhibited the highest removal rate for permanganate index in a static period, which achieved 40.6%. The average removal rates of total nitrogen (TN), ammonia nitrogen (NH3-N) and total phosphorus (TP) in a static period were 23.2, 21.6 and 19.1%, respectively. However, it did not exhibit an excellent removal rate for pollutants in the continuous water diversion period. The average removal rates for all pollutants were below 10%. In winter, the new integrated remediation technology showed efficient effects compared to others. The average removal rate for CODMn, TN, NH3-N and TP were 7, 5.3, 7.6 and 6.5%, respectively. Based on our results, the new integrated water remediation technology was highly efficient as a purification system, especially during the static period in winter.

A novel modified A2/O process (MMAO) was developed for nitrogen and phosphorus removal of municipal sewage. Bench-scale study was conducted to evaluate the performance of the MMAO process treating practical municipal sewage at normal temperature. Activated sludge model (ASM2D) was used to simulate the MMAO process and optimize its design and operation. It was found that the average treatment efficiency of COD, TN, NH4+-N and TP achieved by MMAO were up to 85.7%, 66.8%, 97.35% and 78.1%, respectively. When influent COD concentration of the system was more than 300 mg/L, a better nitrogen and phosphorus removal efficiency of 70% and 90% were achieved. After being calibrated and validated by the experimental results, the activated sludge model of MMAO could simulate the biological reactions occurred in the systems excellently. Optimization design and operational parameters could be accomplished by the mechanical activated sludge modeling. Furthermore, the model could also evaluate the process performance under peak load and low temperature and presented a whole scheme toward the unit combination and operation control. The effluent quality of MMAO process under stable operating could reach the first (B) standard of Municipal Sewage Treatment Plant Pollutants Discharge Standards (GB 18918-2002). The effluent of anaerobic unit was pumped directly into the anoxic unit to supply carbon source for denitrification instead of internal recirculation of mixture liquid, which would save operation cost significantly. The total hydraulic retention time of MMAO was lower than traditional biological organic removal system, so it was very suitable for the improvement of existing plant.