Effects of iron and calcium carbonate on the variation and cycling of carbon source in integrated wastewater treatments

Enhancing the pollutant removal performance and biological mechanisms by adding ferrous ions into aquaculture wastewater in constructed wetland

Aquaculture wastewater seriously threatens the human health. In this study, non-poisonous iron was added into constructed wetlands to purify aquaculture wastewater and the wastewater treatment performances of CWs were explored under the treatment conditions of different plant species and different dosages of ferrous ions. The optimal treatment conditions were experimentally determined as follows: 20 mg/L ferrous ions in CWs planted with Canna indica after 7-day operation, the removal efficiencies of TN, TP and COD were respectively 95 ± 1.9%, 77 ± 1.2% and 62 ± 2%. The improvements in the pollutant removal performance depended on biological mechanisms of plants and microorganisms. The optimal dosage of iron ions could adjust enzyme activities and functional amino acids. Specific functional bacteria (Paracoccus detected based on nirK genetic information and Hydrogenophaga detected based on pufM genetic information) were cultured and domesticated by iron ions. The functional bacteria promoted nitrogen and phosphorus removals.

Influences of Iron Compounds on Microbial Diversity and Improvements in Organic C, N, and P Removal Performances in Constructed Wetlands

The effects of various combinations of iron compounds on the contaminant removal performance in constructed wetlands (CWs) were explored under various initial iron concentrations, contaminant concentrations, different hydraulic retention time (HRT), and different temperatures. The Combo 6 (nanoscale zero-valent iron combined with Fe³⁺) in CW treatments showed the highest pollutant removal performance under the conditions of C2 initial iron dosage concentration (total iron 0.2 mM) and I2 initial contaminant concentration (COD:TN:TP = 60 mg/L:60 mg/L:1 mg/L) in influent after 72-h HRT. These results were directly verified by two different microbial tests (Biolog test and high-throughput pyrosequencing) and microbial community analysis (principal component analysis of community-level physiological profile, biodiversity index, cluster tree, relative abundance at order of taxonomy level). Specific bacteria related to significant improvements in contaminant removal were domesticated by various combinations of iron compounds. Iron dosage was advised as a green, new, and effective option for wastewater treatment. Graphical Abstract .

Enhanced Simultaneous Nitrogen and Phosphorus Removal in A Denitrifying Biological Filter Using Waterworks Sludge Ceramsite Coupled with Iron-Carbon

In this study, waterworks sludge ceramsite (WSC) was combined with 3% iron-carbon matrix in a denitrifying biological filter (ICWSC-DNBF) to enhance the simultaneous removal of carbon, nitrogen and phosphorus in secondary effluent of wastewater treatment plant (SE-WTP). The chemical oxygen demand (COD) and nitrogen removal, as well as phosphorus removal and the adsorbed forms of phosphorus were measured and the removal mechanism of these pollutants by the ICWSC-DNBF system for treating SE-WTP were investigated. The results showed that the ICWSC-DNBF achieved good removals of COD, NH₄⁺-N, NO₃^--N, total N and total P; effluent concentrations were 17.23 mg/L, 3.72 mg/L, 14.32 mg/L, 17.38 mg/L and 0.82 mg/L, respectively. WSC enhanced the P removal due to its high specific surface area and the high number of adsorption sites. Fe-P and Al-P were the main forms of P adsorbed by WSC, accounting for 78.53% of the total adsorbed P. WSC coupled with Fe and C improved the biodegradability of SE-WTP and promoted the removal of organic matter. The removal of N was attributed to the abundant denitrifying microorganisms in the system and the electrochemical effect produced by the internal electrolysis of Fe and C.

Effect of corn cobs as external carbon sources on nitrogen removal in constructed wetlands treating micro-polluted river water

Micro-polluted river water is characterized as having limited biodegradability, low carbon to nitrogen ratio and little organic carbon supply, all of which makes it hard to further purify. Two bench scale constructed wetlands (CWs) with a horizontal subsurface flow mode were set up in the laboratory to evaluate their feasibility and efficiency on denitrification with and without corn cobs as external carbon sources. Micro-polluted river water was used as feed solution. The CW without corn cobs substrates possessed a good performance in removing chemical oxygen demand (COD, <40 mg/L) and ammonia nitrogen (NH₃-N, <0.65 mg/L), but less efficiency in removing total nitrogen (TN) and nitrate nitrogen (NO₃-N). In marked contrast, the CW with 1% (w/w) corn cobs substrates as external carbon sources achieved a significant improvement in the removal efficiency of TN (increased from 34.2% to 71.9%) and NO₃-N (increased from 19% to 71.9%). The incorporation of corn cobs substrates did not cause any obvious increase in the concentrations of COD and NH₃-N in the effluent. This improvement in the denitrification efficiency was owing to the released organic carbon from corn cobs substrates, which facilitated the growth of abundant microbes on the surface and pores of the substrate. The open area of the used corn chips is larger than that of the pristine ones, and corn cobs can continue to provide a carbon fiber source for denitrification.

Addition of iron materials for improving the removal efficiencies of multiple contaminants from wastewater with a low C/N ratio in constructed wetlands at low temperatures

Constructed wetlands (CWs) are widely used in wastewater treatment. Wastewater generally contains multiple contaminants. In this study, CWs were applied to treat wastewater with a low COD/TN ratio and containing heavy metals. Iron-based material was added in CWs to enhance the treatment efficiency. The contaminant removal efficiency was positively correlated with the dosage of iron-based material. Considering the operation cost, we added 1 g of iron-based material in CW and realized the multi-contaminant removal efficiency after 4-day treatment at low temperature: 99.51% of Cu(II), 87.22% of Cr(VI), 65.62% of TN, and 60.23% of COD. Microbial community analysis and kinetic analysis predicted that the removal mechanism involved ion exchange and microbial denitrification. Specific bacteria were found in CWs with iron-based material, such as Thiobacillus spp. and Thauera spp., indicating that the nitrate removal in the denitrification process was triggered by carbon sources and that Fe²⁺ worked as both the electron donor and the adjuster of the abundances of specific bacteria. The addition of iron-based material into CWs was a green option to improve the pollutant removal performance.

Effects of iron and calcium carbonate on contaminant removal efficiencies and microbial communities in integrated wastewater treatment systems

In the paper, we explored the influences of different dosages of iron and calcium carbonate on contaminant removal efficiencies and microbial communities in algal ponds combined with constructed wetlands. After 1-year operation of treatment systems, based on the high-throughput pyrosequencing analysis of microbial communities, the optimal operating conditions were obtained as follows: the ACW10 system with Fe³⁺ (5.6 mg L^-1), iron powder (2.8 mg L^-1), and CaCO₃ powder (0.2 mg L^-1) in influent as the adjusting agents, initial phosphorus source (PO₄^3-) in influent, the ratio of nitrogen to phosphorus (N/P) of 30 in influent, and hydraulic retention time (HRT) of 1 day. Total nitrogen (TN) removal efficiency and total phosphorus (TP) removal efficiency were improved significantly. The hydrolysis of CaCO₃ promoted the physicochemical precipitation in contaminant removal. Meanwhile, Fe³⁺ and iron powder produced Fe²⁺, which improved contaminant removal. Iron ion improved the diversity, distribution, and metabolic functions of microbial communities in integrated treatment systems. In the treatment ACW10, the dominant phylum in the microbial community was PLANCTOMYCETES, which positively promoted nitrogen removal. After 5 consecutive treatments in ACW10, contaminant removal efficiencies for TN and TP respectively reached 80.6% and 57.3% and total iron concentration in effluent was 0.042 mg L^-1.