Physicochemical and microbiological characterization of human faeces and urine from composting toilets in Abidjan, Côte d'Ivoire.

We assessed the physicochemical and microbiological properties of composting toilet products in Abidjan for their potential use in agriculture. Samples of urine and faeces were collected and analysed after 123 days of storage in plastic cans (urine) and 8 months of storage in closed composting bags (faeces). Selected physicochemical parameters (ammonium, phosphorus, potassium, calcium, magnesium) and pathogens (bacteria and helminths eggs) were monitored. Results showed that temperature and pH values were 26.0°C and 7.2, and 27.6°C and 8.6 for the faeces and urine, respectively. The physicochemical analysis revealed high nutrient contents and low trace metal levels in the faeces-based compost. Concentrations of magnesium, cadmium, copper, lead and zinc ranged from 0.46 to 54.98 mg/kg; while those of phosphorus, potassium and calcium were >700 mg/kg on average. In urine, the concentrations of phosphorus, potassium, calcium, copper and zinc were 930, 1240, 1402.8, 0.0672 and 0.121 mg/L, respectively. Various bacteria (including total coliforms, faecal coliforms, faecal streptococci and anaerobic sulphite reducers), along with Ascaris lombricoïds (1.66 eggs/g), were found in the faeces-based compost. Our findings indicate that the faeces-based compost was not homogeneous, namely with regard to the microbiological parameters, and additional time would be necessary to bring it to stability.

Predicting the effects of chlorine on the micro-organisms of filamentous bulking activated sludges.

Rapid and definite assessment of the effect that a specific biocide has on a specific case of filamentous bulking sludge is a much-needed tool in activated sludge wastewater treatment. The Live/Dead stain (LIVE/DEAD BacLight) distinguishing "living" and "non-living" cells, a nitrifying activity (NA) test and the oxygen uptake rate (OUR) measurement were examined for their appropriateness to predict the effects of chlorine on filamentous bulking sludges. The study showed the live/dead stain to be relevant for revealing the specific effect of chlorine on the filamentous bacteria of a bulking sludge. However, using live/dead stain alone for the determination of the appropriate chlorine dose against bulking may lead to an underestimation of the damage caused by chlorine to the useful microorganisms in the flocs. Indeed, using the live/dead stain, it was not easy to distinguish dead cells caused by chlorination from those originally present in the flocs The NA test was the most sensitive in detecting damage caused by chlorine to the floc-forming microorganisms. Therefore, for a safer determination of the chlorine dose effective against bulking and protective of the microbial activity of the sludge, the results of this study suggest coupling of the live/dead stain with the NA test and/or the OUR test.

Full-scale evaluation of a multi-component additive for efficient control of activated sludge filamentous bulking.

A multi-component additive formulated for a more efficient control of activated sludge filamentous bulking was evaluated at a full-scale treatment plant experiencing severe filamentous bulking. It was found that, besides offering an immediate improvement of sludge settling, the multi-component additive was able to eliminate the filamentous bacteria causing the bulking. Hence, contrary to ordinary additives, this novel additive yielded immediate as well as long-term improvements in sludge sedimentation upon a few additions. Preliminary lab-scale toxicity tests showed that the treatment of the sludge by the additive should not impart any toxicity to the resulting effluent.

Chlorine-susceptible and chlorine-resistant type 021N bacteria occurring in bulking activated sludges.

Two filamentous bacteria causing bulking in two activated sludges were examined. Investigations using morphological features, staining techniques, and fluorescent in situ hybridization identified both filaments as type 021N. However, an examination of the effect of chlorine on the sludges revealed a chlorine-susceptible type 021N in one sludge and a chlorine-resistant type 021N in the other.

A test for predicting propensity of activated sludge to acute filamentous bulking.

Filamentous bulking is a solid-liquid separation problem well known to activated-sludge plant operators. The use of curative additives is a rather delicate solution and the tools developed to anticipate it seem limited. To complement existing sludge sedimentation monitoring tools, a new test to assess the propensity of activated sludge for filamentous bulking was developed. It consists of challenging the sludges by feeding them under conditions favoring filamentous bacteria for 24 hours. The effects of such an acute treatment on sludge settleability is subsequently assessed through a simple sludge volume (SV30) measurement with reference to a control. The sludge can then be evaluated as prone to bulking (unstable sludge) or not (stable sludge). Such a test can be used to predict the occurrence of filamentous bulking in activated-sludge treatment plants. This so-called acute bulking test requires simple equipment and can be done by any wastewater treatment plant operator.

Efficient control of activated sludge filamentous bulking by means of a multi-component additive.

A multi-component additive formulated for a more efficient control of activated sludge filamentous bulking was evaluated at a full-scale treatment plant experiencing a severe filamentous bulking. It was found that, besides offering an immediate improvement of sludge settling, the multi-component additive was able to eliminate the filamentous bacteria causing the bulking. Hence, contrarily to ordinary additives, this novel additive yielded immediate as well as long-term improvement of sludge sedimentation upon a few additions.