New progress of ammonia recovery during ammonia nitrogen removal from various wastewaters.

The recovery of ammonia-nitrogen during wastewater treatment and water purification is increasingly critical in energy and economic development. The concentration of ammonia-nitrogen in wastewater is different depending on the type of wastewater, making it challenging to select ammonia-nitrogen recovery technology. Meanwhile, the conventional nitrogen removal method wastes ammonia-nitrogen resources. Based on the circular economy, this review comprehensively introduces the characteristics of several main ammonia-nitrogen source wastewater plants and their respective challenges in treatment, including municipal wastewater, industrial wastewater, livestock and poultry wastewater and landfill leachate. Furthermore, we introduce the main methods currently adopted in the ammonia-nitrogen removal process of wastewater from physical (air stripping, ion exchange and adsorption, membrane and capacitive deionization), chemical (chlorination, struvite precipitation, electrochemical oxidation and photocatalysis) and biological (classical and typical activated sludge, novel methods based on activated sludge, microalgae and photosynthetic bacteria) classification based on the ammonia recovery concept. We discuss the applicable methods of recovering ammonia nitrogen in several main wastewater plants. Finally, we prospect the research direction of ammonia removal and recovery in wastewater based on sustainable development.

Effects of microwave heating on the protein structure, digestion properties and Maillard products of gluten.

As a kind of traditional food, gluten is widely studied for its physical and chemical properties after processing, while little attention is paid to the simulation cooking processing, digestion and safety. In this paper, gluten was heated with microwave to study its structural transformations, nutritional efficiency, and food safety under Chinese home cooking (CHC). After microwave treatment, intermolecular and intramolecular cross-linking of gluten were formed to result in more aggregation. The secondary structure of gluten changed significantly as well as the formation of α-helix and ß-turn promoted under the high power input. Treated with 1000 W for 5 min, cross-linking between amino acids increased, leading the reduction of total amino acids, in vitro protein digestibility and the increase of high molecular weight peptides, while the proportion of essential amino acids kept the same. In the simulation of CHC, the highest content of 5-hydroxymethyl furfural was observed after adding all condiments under 1000 W for 5 min. In addition, sugar played a major role in Maillard reaction to promote the formation of melanoidin and fructosamine while salt and oil did not significantly affect these two Maillard products. Vinegar inhibited the reaction due to the acidic condition but provided some melanoidin and fructosamine itself.

The combination of aerobic and microaerobic promote hydrolysis and acidification of rice straw and pig manure: Balance of insoluble and soluble substrate.

Separated hydrolysis and acidification is an effective pretreatment method for anaerobic digestion of lignocellulose. However, excess consumption of soluble substrates remains a problem. Rice straw and pig manure were used as substrates with biogas slurry as the inoculum, combined with aerobic and microaerobic conditions in the 14-day hydrolysis and acidification. Aeration can significantly accelerate volatile solid degradation (38.25%), especially the lignocellulose. Soluble chemical oxygen demand (29157 mg/L) and volatile fatty acids (13219 mg/L) of the group with 4 days aerobic treatment, reached their peaks on day 5, obtaining a balanced insoluble substrate degradation and soluble substrate consumption. Candida, Lactobacillus, Bifidobacterium, and Acetobacter were enriched at the balanced point for positive contribution to the degradation of the insoluble substrate and the generation of soluble substrate. This study not only reveals the balance between degradation and consumption, but also provides new insight into biogas slurry recycling and anaerobic digestion precursor substrate production.

Effect of chlortetracycline on the growth and intracellular components of Spirulina platensis and its biodegradation pathway.

Chlortetracycline (CTC) usually presents in livestock wastewater with oxytetracycline (OTC), causing damage to human health and ecosystems. It's urgent to seek low-cost and ecofriendly technology for antibiotics removal. In this study, effects of CTC and CTC + OTC (CTC:OTC= 1:1, g/g) on Spirulina platensis have been investigated. EC50 value of CTC for S. platensis was 8.76 mg/L at 96 h and risk quotient value in wastewater was 15.85. Inhibition of CTC on S. platensis gradually enhanced with increase of CTC, but CTC + OTC below 1.0 mg/L didn't harm the growth of microalgae. Chlorophyll-a (Chl-a) and carotenoid content showed a parabolic trend with extension of time at CTC group. Chl-a synthesis gradually decreased with increase of CTC + OTC stress. High concentrations of CTC and CTC + OTC showed obvious inhibition on phycocyanin production. Polyunsaturated fatty acids (PUFA) and saturated fatty acids (SFA) contents peaked at 1.0 mg/L CTC, corresponding to the minimum of superoxide dismutase (SOD) activity in S. platensis. SFA and PUFA contents decreased when CTC + OTC content was above 2.0 mg/L. CTC and CTC + OTC (both over 2.0 mg/L) stimulated production of dissolved extracellular organic matters in S. platensis. Removal efficiency of CTC by S. platensis was about 98.63-99.95% and its biodegradation pathways were hydroxylation and side-chain breakdown.

Preparation and characteristics of bentonite-zeolite adsorbent and its application in swine wastewater.

The preparation of bentonite-zeolite (BZ) adsorbent using bentonite, aluminate, and rice husk was conducted. The adsorption experiment was performed for the removal of Cu2+ and Zn2+ from aqueous solution in single and binary systems. Results showed that gasification of rice husk could effectively improve the specific surface area and pore volume. The optimum pH for Cu2+ and Zn2+ adsorption on BZ was pH 5.0. The pseudo-first order kinetic and Langmuir isotherm model of BZ were the optimal model for Cu2+ and Zn2+. According to Langmuir isotherm model, the maximum adsorption capacity value (qm) was 16.39 and 12.72 mg·g-1 for Cu2+ and Zn2+, respectively. The adsorption affinity order of BZ in the binary solution was Cu2+ > Zn2+. NH4+-N concentration over 500 mg·L-1 significantly affected the adsorption capacity of BZ (P < 0.05). The adsorption capacity of BZ for Cu2+ and Zn2+ was higher than that artificial zeolite (AZ) and bentonite in SW.

Nutrient removal from digested swine wastewater by combining ammonia stripping with struvite precipitation.

Typical biological processing is often challenging for removing ammonia nitrogen and phosphate from swine wastewater due to inhibition of high ammonia on activity of microorganisms, exhaustion of time, and low efficiency. In this study, a physicochemical process by combining ammonia stripping with struvite precipitation has been tested to simultaneously remove ammonia nitrogen, phosphate, and chemical oxygen demand (COD) from digested swine wastewater (DSW) with high efficiency, low cost, and environmental friendliness. The pH, temperature, and magnesium content of DSW are the key factors for ammonia removal and phosphate recovery through combining stripping with struvite precipitation. MgO was used as the struvite precipitant for NH4+ and PO43- and as the pH adjusted for air stripping of residual ammonia under the condition of 40 °C and 0.48 m3 h-1 L-1 aeration rate for 3 h. The results showed that the removal efficiency of ammonia, total phosphate, and COD from DSW significantly increased with increase of MgO dosage due to synergistic action of ammonia stripping and struvite precipitation. Considering the processing cost and national discharge standard for DSW, 0.75 g L-1 MgO dosage was recommended using the combining technology for nutrient removal from DSW. In addition, 88.03% NH4+-N and 96.07% TP could be recovered from DSW by adsorption of phosphoric acid and precipitation of magnesium ammonium phosphate (MAP). The combined technology could effectively remove and recover the nutrients from DSW to achieve environmental protection and sustainable and renewable resource of DSW. An economic analysis showed that the combining technology for nutrient removal from DSW was feasible.

Evaluation of ammonia recovery from swine wastewater via a innovative spraying technology.

An innovative spraying system for NH4+-N removal and recovery was investigated under different pH, temperature, spraying frequency and rate by using spraying system. Results showed that NH4+-N removal efficiency and mass transfer coefficient (KLa) value in swine wastewater (SW) remarkably increased with increasing of temperature, spraying frequency and rate due to promoting the diffusion of NH3 molecules caused by increasing specific surface of SW molecule, and high shear force and temperature difference between SW and circulating heating tube. Considering the cost and discharge standard, the optimum parameters for NH4+-N removal from SW using spraying system were alkaline, 0.24 m3 h-1 of continuous spraying, and 45 °C circulating water, and the NH4+-N decreased from 591.2 to 68.9 mg L-1 (<80 mg L-1) after 8 h treatment, and this value corresponded to 88.35% removal rate. Furthermore, over 85% recovery rate for NH4+-N could be obtained through absorption of phosphoric acid.

Characterization of additional zinc ions on the growth, biochemical composition and photosynthetic performance from Spirulina platensis.

In this study, the effect of various initial Zn2+ concentration additionally on microalgae growth and biochemical composition were investigated. The Spirulina platensis biomass of each concentration reached the maximum at the end of the cultivation. However, high levels could severely inhibit the growth of microalgae. Fluorescence activity occurred changes in response to heavy metal stress. Moreover, biochemical composition in Spirulina platensis altered under zinc stress, and the highest contents of phycocyanin (PC), Chlorophyll-a (Chl-a), Carotenoid and zinc accumulation were obtained. The proportion of saturated and polyunsaturated fatty acids increased constantly in response to Zn2+ exposure. Overall, this study indicated that the use of Spirulina platensis is a viable method for treating zinc containing wastewater and harvested microalgae can be processed into high-zinc products.