No abstract

No abstract

No abstract

Partial nitritation providing a suitable effluent for subsequent anammox is a critical step in a two-stage autotrophic nitrogen removal system. This study demonstrates an innovative approach for attaining partial nitritation in an acidic bioreactor operating at a slightly low pH (i.e., 5–6). This approach is based on our hypothesis in this study that acid-tolerant ammonia-oxidizing bacteria (AOB) can produce nitrite and protons to self-sustain free nitrous acid (FNA, NO2 – + H+ ↔ HNO2) at a parts per million level, as an inhibitor of nitrite-oxidizing bacteria (NOB). With influent nitrogen of about 200 mg/L and operating conditions of high dissolved oxygen, long sludge retention time, and moderate temperature, a lab-scale acidic bioreactor with FNA up to 2 mg of HNO2-N/L successfully established stable nitrite accumulation in the effluent for 200 days, with an average ratio [NO2 –/(NO2 – + NO3 –)] exceeding 95%. A 16S rRNA amplicon sequencing analysis showed that Nitrosospira was the dominant AOB in the biomass of the bioreactor, while Nitrosomonas and Nitrospira, two typical nitrifying genera in neutral wastewater treatment, both disappeared after the startup of partial nitritation. Kinetic characterization revealed that Nitrosospira had a substrate affinity of 11.4–16.5 mg of total ammonia (NH4 + + NH3)/L. It also revealed that less than 3.5 mg of HNO2-N/L FNA did not inhibit AOB activity significantly. Acidic operation is economically attractive because it can be achieved via acidophilic ammonia oxidation without adding chemical acid. However, hazardous gas, nitric oxide (NO), should be removed from gas produced by acidic nitrifying bioreactors.

No abstract

No abstract

Recycle domestic greywater for on-site non-potable uses can lessen the demand on potable water and the burden on wastewater treatment plants. However, lack of studies to assess health risk associated with such practices has hindered their popularity. A Quantitative Microbial Risk Assessment was conducted to estimate the public health risks for two greywater reuse scenarios: toilet flushing and food-crop irrigation. Household greywater quality from three sources (bathroom, laundry and kitchen) was analyzed. Mathematical exposure rates of different scenarios were established based on human behavior using Monte-Carlo simulation. The results showed that, greywater from all three household sources could be safely used for toilet flushing after a simple treatment of microfiltration. The median range of annual infection risk was 8.8 × 10−15–8.3 × 10−11 per-person-per-year (pppy); and the median range of disease burden was 7.6 × 10−19–7.3 × 10−15 disability-adjusted life years (DALYs) pppy. In food-crop irrigation scenario, the annual infection risks and disease burdens of treated greywater from bathroom and laundry (2.8 × 10−8, 4.9 × 10−8 pppy; 2.3 × 10−12–4.2 × 10−12 DALYs pppy) were within the acceptable levels of annual infection risk (≤10−4 pppy) and WHO disease burden (≤10−6 DALYs pppy) benchmarks, while kitchen greywater was not suitable for food-crop irrigation (4.9 × 10−6 pppy; 4.3 × 10−10 DALYs pppy) based on these benchmarks. The model uncertainties were discussed, which suggests that a more accurate risk estimation requires improvements on data collection and model refinement.

This study investigated the recovery of N, P and K from source-separated urine in laboratory-scale combined processes of air stripping and precipitation. Two operation scenarios were carried out to recover N/P (named partial scenario) and N/P/K (named complete scenario). Most of the nutrients were recovered (>70%) by optimising the operation parameters including the increase of air flow rate and more dosages of the sources of Mg and P. Absorbent rich in ammonium sulphate and solid precipitates including struvite, struvite-K, and struvite-Na was produced. The simultaneous recovery of P and K was the key process to determine the substance input. The ratio of substance input to nutrient recovered (PO and KO) was 4.14 in the partial scenario, whereas it increased to 10.61 in the complete scenario. The inevitable co-precipitation of struvite-Na mainly responded for the lower economic efficiency of the complete scenario.