To enhance the reducing sugar yield in enzymatic hydrolysis, various factors (NaOH concentration, solid content and pre-treatment time) that affect the pre-treatment process were investigated and ...evaluated based on the reducing sugar yield of the subsequent enzymatic hydrolysis. The enzymatic hydrolysis was based on the cellulase from Trichoderma reesi ATCC 26921, the optimum NaOH pre-treatment conditions were an NaOH concentration of 1.0% (w/w), a solid content of 5.0% (w/v) and a pre-treatment time of 60 min. Various parameters that affect the enzymatic hydrolysis of wheat straw, including the solid content, enzyme loading, pH and hydrolysis time, were investigated and optimized through a Box-Behnken design and response surface methodology. The predicted optimum conditions for enzymatic hydrolysis were a solid content of 8.0% (w/v), an enzyme loading of 35 FPU/g substrate, a temperature of 50 °C, a pH of 5.3 and a hydrolysis time of 96 h. The experimental result showed that the maximum reducing sugar yield was 60.73% (53.35% higher than the wheat straw without NaOH pre-treatment), which is in accordance with the predicted conditions.
Constructed ditch wetland (CDW) is a combination of idle ditch and constructed wetland, which is typically used in rural areas to remove pollutants from domestic wastewater. However, its low total ...nitrogen (TN) removal remains a pressing issue. To enhance total nitrogen removal, an approach of supplying water at two locations in the CDW at different influent flow ratios, combined with artificial aeration, was proposed to adjust carbon and oxygen distribution in the system. The highest average TN removal was achieved at low influent concentration (CDW4; influent flow ratio 1:2). The removal of TN in winter and spring were 58.93 and 83.26%, respectively. The distribution of carbon sources in the back zone enhanced denitrification. Of the high influent concentration treatments, CDW2 (2:1) achieved 16.97% more TN removal on average compared with CDW1 (3:0), after extra artificial aeration was applied in the front zone. However, nitrification was a limiting step in the system, which became the primary problem preventing pollutant purification. Moreover, nitrifying bacteria abundance was negatively correlated to the influent flow ratio and autotrophic denitrifying bacterial abundance was positively correlated to the influent flow ratios.
Graphical abstract
Constructed wetlands (CWs) are characterized by low construction cost, convenient maintenance and management, and environmentally friendly features. They have emerged as promising technologies for ...decentralized sewage treatment across rural areas. Source separation of black water and gray water can facilitate sewage recycling and reuse of reclaimed water, reduce the size of treatment facilities, and lower infrastructure investment and operating cost. This is consistent with the concept of sustainable development. However, black water contains high concentrations of ammonia nitrogen, and the denitrification capacity of CWs is not excellent due to insufficient carbon source. Therefore, application of CWs for black water treatment faces challenges. This article provides a review on the progress in CWs for treatment of the sewage with high-influent nitrogen load, with emphasis on the commonly used strengthening means and the role of plants in nitrogen removal via CWs. The current issues of rural sewage treatment with high-influent nitrogen load by CWs are also assessed. Finally, the challenges and perspectives are discussed for the optimization of CWs-enhanced denitrification strategies.
Graphic abstract
Algal ponds (APs) are widely used as treatment facilities for domestic sewage in sparsely populated rural areas. However, few AP studies have focused on daylight length to enhance pollutants removal. ...In this study, four algae ponds were set up, daylight was prolonged by 0, 2, 4, and 6 h with an illuminating intensity of 3000 lx. The highest removal efficiencies of total nitrogen, ammonium, and total phosphorus were 37.36%, 41.20%, and 21.56% due to the highest microbial abundance under optimum conditions (2 h PD), respectively. Excessive PD (4 h and 6 h) could inhibit the removal abilities. PD also increased the maximum relative electron transport rate of algae, leading to an increase in the photosynthetic capacity of APs. Meanwhile, the high microbial abundance indicates that chemoheterotrophic bacteria are the main influencing factor for the removal of nitrogen and phosphorus by the APs. Moreover, the system with PD using artificial lamps was proven to be feasible for engineering applications and potentially utilized in rural domestic wastewater treatment.
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•Four prolonged daylight (PD) scenarios were tested in algal ponds.•Excessive PD (more than 2 h) could decrease TN and TP removal.•PD affected algal photosynthetic capacity which indirectly influence N and P removal.•Abundance of chemoheterotrophic bacteria could decisively impact N and P removal.•Algal ponds with LED lamps for PD are feasible and efficient.
Hyperthermophilic microorganisms play a key role in the hyper-thermophilic composting (HTC) technique. However, little information is available about the hyperthermophilic microorganisms prevalent in ...HTC systems, except for the
Calditerricola satsumensis
,
Calditerricola yamamurae
, and
Thermaerobacter
. To obtain effective hyper-thermophilic microorganisms, a continuous thermo-acclimation of the suitable thermophilic microorganisms was demonstrated in this study.
Bacillus thermoamylovorans
with high-temperature endurance (70 °C) were newly isolated from sludge composting, and an adequate slow heating rate (2 °C per cycle) was applied to further improve its thermostability. Finally, a strain with a maximum growth temperature of 80 °C was obtained. Moreover, structural and hydrophobic changes in cell proteins, the special amino acid content ratio, and the membrane permeability of the thermophilic bacterium after thermo-acclimation were evaluated for improved thermostability. In addition, the acclimated hyperthermophilic bacterium was further inoculated into the HTC system, and an excellent performance with a maximum operating temperature of 82 °C was observed.
Graphic abstract
Living Machine (LW) was principle technology in the treatment of source-separated blackwater for resource recovery. In this study, three Living Machine (LM) systems planted with different ...phytocoenoses were operated in parallel to investigate the removal performance of blackwater from septic tank. Higher removal efficiency of turbidity, COD, NH
4
+
-N, TN, and TP of 98.2%, 88.7% 86.5%, 61.2%, and 41.3%, respectively, was obtained in system 1. The floristics with better tolerance and reduction capacity of blackwater in five tanks were listed as follows:
Canna indica
L.,
Cyperus alternifolius,
and
Arundo donax
var.
versicolor
Stokes of tank 3;
Polygonum chinense
L.,
Scirpus validus
Vahl,
Pontederia cordata
L.,
Setcreasea pallida,
and
Hydrocotyle chinensis
(Dunn) Craib of tank 4; and
Myriophyllum verticillatum
L. and
Spirodela polyrhiza
(L.) Schleid. of tank 5. Overall, the LM system with suit plant groups offered a more sustainable and economical solution for treating blackwater.
Blackwater constitutes a primary component of environmental pollution posing serious risk to human health; however, reusing the nutrients found in blackwater diminishes the associated pollution and ...promotes resource recycling. Conventional green-wall systems are not suitable for in situ treatment of high-concentration wastewater. Thereby, a novel multi-unit green-wall system with six independent treatment units was designed to achieve a cost-effective and eco-friendly in situ treatment of blackwater with high organic load. Zeolite carriers were selected for the matrix with carrier depth of 14.5 cm, ivy and chlorophytum were selected as the greening plants. Various pollutants were rapidly reduced at the initial stage and the concentration of the pollutants decreased as the number of treatment units increased. Overall, the green-wall system was more effective in removing COD and NH
4
+
–N with the removal rates of 98.5% and 98%, which may be due to the good buffering capacity of the media and the roles of
Firmicutes
and
Bacteroidetes
in COD degradation and ammoniated nitrification reactions. In addition, the maximum TP and TN removal rates were observed with a value of 85% and 42%, respectively. Consequently, the novel multi-unit green-wall system is an effective method for in situ blackwater reuse.
Graphical Abstract
Surfactants, especially non-ionic surfactants, play an important role in the preparation of nanocarriers and can also promote the enzymatic hydrolysis of lignocellulose. A broad overview of the ...current status of surfactants on the immobilization of cellulase is provided in this review. In addition, the restricting factors in cellulase immobilization in the complex multiphase hydrolysis system are discussed, including the carrier structure characteristics, solid-solid contact obstacles, external diffusion resistance, limited recycling frequency, and nonproductive combination of enzyme active centers. Furthermore, promising prospects of cellulase-oriented immobilization are proposed, including the hydrophilic-hydrophobic interaction of surfactants and cellulase in the oil-water reaction system, the reversed micelle system of surfactants, and the possible oriented immobilization mechanism.
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•Iron scraps enhance simultaneous total nitrogen and total phosphorus removal.•Iron scraps enhanced nitrification and autotrophic denitrification process.•Main phosphorus removed by ...FeOOH adsorption.
In rural domestic wastewater treatment using subsurface constructed wetland system (SFCWs), the lack of a carbon source for denitrification and limited phosphorus uptake are responsible for low removal of nitrogen and phosphorus, and a suitable substrate is therefore, necessary. Iron is an important component in nitrogen and phosphorus biogeochemical cycles. Few studies have addressed the application of iron in SFCWs. Therefore, we constructed SFCWs that used iron scraps as a substrate. Enhanced nitrification, denitrification and removal of phosphorus were observed. The large proportion of nitrite-oxidising bacteria present in CWs with iron scraps (CW-T) compared to gravel beds indicated that iron may enhance ammonium (NH4+) oxidation. More nitrate-reducing bacteria related to Fe and autotrophic denitrifying bacteria were discovered in the back zone of CW-T and these enhanced denitrification process. Phosphate (PO43−) reacted with ferrous ion (Fe2+) and ferric ion (Fe3+) to generate the precipitant. Moreover, Fe3+ reacted with water to generate iron oxide (FeOOH) that had a large adsorption capacity for phosphorus. After six months of operation, average NH4+-N, total nitrogen and total phosphorus removal rates were 66.98 ± 13.37 %, 71.26 ± 13.57 % and 93.54 ± 6.64 %, respectively. Iron scraps can potentially be utilised in SFCWs in rural domestic wastewater treatment.
Constructed wetlands (CWs) are a sustainable technology used to remove pollutants from wastewater; however, their low total nitrogen (TN) removal efficiency remains a pressing issue. Constructed ...ditch wetland systems (CDWs) differ from CWs in being narrow and shallow. This study observed the performance of CDWs throughout their operational period and investigated the causes of their low TN removal rates. To enhance TN removal, we propose an approach where the inflow is divided into two parts with different influent flow ratios. Four systems were trialed in parallel to examine the effects of the influent flow ratio distribution on organics removal and nitrogen transformation. A flow ratio of 1:2 was considered optimal following comparison of the four experimental CDWs. The removal efficiencies of chemical oxygen demand (COD) and TN in the control CDW (influent flow ratio 3:0) during winter were 91.15% and 25.87%, respectively, whereas the removal efficiencies of the best-performing CDW (influent flow ratio 1:2) were 91.59% and 50.40%, respectively. Based on an analysis of nitrogen transformation, a model of effluent TN and nitrate nitrogen concentration in the four CDWs was constructed.
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•A CDWs combining ditch and constructed wetland was built up to treat decentralized domestic wastewater.•The CDWs has both functions of collection and treatment for decentralized domestic wastewater in rural areas.•The decentralized inflow method can solve the problem of carbon shortage for denitrification.•A simple formula quantified the nitrogen removal process of the decentralized inflow CDWs.
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